A comprehensive overview of functional and rheological properties of aloe vera and its application in foods

Abstract

Aloe vera catches attention of food industry due to its various health benefits like emollient, anti-inflammatory, purgative, anti-microbial, aphrodisiac, antifungal, and antioxidant. Aloe vera gel has excellent functional and nutritional properties and its incorporation into food can increase its functional and nutritional value of the food. However, both the pulp and aloe gel contain a lot of insoluble polymer particles, which affect the rheological behaviour and physical stability mechanisms of the suspensions during storage and processing. While many researchers have explored the application of aloe vera juice in the food products, no literature review of food applications of aloe vera along with their rheological properties have been complied. Hence, the present review aimed to focus on the utilization of aloe vera in the various sectors of food processing and gives insights on the rheological and flow behaviour of aloe vera juice which is a critical parameter for its food application.

Introduction

Aloe vera, commonly known as Gheegwar/Ghritkumari and scientifically known as Aloe barbadensis belongs to family Lilaceae. Aloe is derived from Arabic word “alloeh” which means “bitter”. It is a nature gifted plant popular for its herbal remedy. Hence, often called as miracle plant (Rjasekaran et al. 2005). The dry and hot climates like deserts are most favorable condition for the growth of aloe vera plant. The therapeutic and functional properties of aloe vera has increased its use in the new food product design (Campestrini et al. 2013).

Nowadays, consumers look for the wholesome nutrition where it should not only fulfil the satiety but also have preventive against disease (Fernandes et al. 2018). Thus, balanced nutrients with functional and health benefits are focused by consumers. This has shifted the research focus on plant based food products by using underutilized fruits, vegetables and seeds (Sonawane and Arya 2018). The quickly growing nature of aloe vera catch attention of researcher for bioactive components and their functional properties and health benefits. This review gives insight on application of aloe vera in food fortification with the effect on nutritional and functional quality of products and effect of different processing techniques on the rheological properties of aloe vera which is a critical parameter during its food application.

Anatomy and history of aloe vera

The aloe vera leaves are triangular in shape with 20 × 5 (length and wide) inches, with soft spike with edges and composed with fleshy mucilaginous (Rjasekaran et al. 2005). Basically, three layers are found in aloe vera, where 95% water present in inner layer gel and rest of part is made with lipids, amino acids, sterols, vitamins., and glucomannans. Figure 1 shows morphology of aloe vera leaf. The gel and rind of aloe vera leaves shows the presence of active ingredients which concentrated in inner layer which has significant clinical and pharmacological importance (Rjasekaran et al. 2005). The latex is present in the middle layer which is bitter yellow sap and composed with glycosides and anthraquinones. The rind is an outer layer made with proteins and carbohydrates which almost composed with 15-20 cells. Inside the rind, starch (phloem) and water (xylem) delivered by vascular bundles (Surjushe et al. 2008).

Fig. 1.

Aloe vera plant and schematic representation of aloe leaf morphology (Rahman et al. 2017)

The Barbadensis miller is most widely used aloe vera species, where 300 species of aloe vera are available (Bhuvana et al. 2014). Aloe vera mainly grows in South Texas, Florida, South and Central America, Mexico, India, Africa, South California, Australia, Caribbean and Iran (Verma 2016). In folk medicine, the extract of whole leaf and gel of aloe vera has been used. Improvement in the bioavailability of vitamins when co-administered with aloe vera has been reported by Vinson et al. 2005.

Chemical composition and health benefits of aloe vera

Aloe vera leaf has excellent properties with 95% of water, bioactive compounds, minerals, enzymes, nutrients, vitamins, and amino acids (Banjare et al. 2014). Table 1 shows various chemical compounds, their respective classes and function present in the Aloe vera. The various streams of medicine such as homoeopathic, Allopathic and Ayurvedic have applied aloe vera as medicine due to its therapeutic effects such as emollient, anti-inflammatory, purgative, anti-microbial, aphrodisiac, antifungal, antioxidant and also has cosmetic values (Benzidia et al. 2018), whereas it is consumed as a food by tribal community people.

Table 1.

Summary of the chemical composition of aloe vera

CLASS	Chemical compounds	Function	References
Fatty acids	Diisooctylphtalate (11.84%), phytol (14.40%), linolenic acid (16.59%), and palmitic acid (11.91%)	Antioxidant	Benzidia et al. (2018)
Phytochemicals	Alkaloid, flavonoids, sterols, triterpenes, tannins	Antioxidant, antiradical	Benzidia et al. (2018)
Anthraquinones	Homonataloin B, Aloinoside B, Microdontin B, Aloin B, Aloin A, Microdontin A, Aloinoside A	Laxative, antidiabetic, and antioxidant	Aldayel et al. (2020), Surjushe et al. (2008)
Carbohydrates	Lignins and sugars such as arabinose, cellulose, fructose, fucose, galactose, glucose lactose, maltose, mannose, pectic substance rhamnose, sucrose, uronic acid and xylose	Antidiabetic, antiallergic and anti-inflammatory	Surjushe et al. (2008)
Chromones	Isorabaichromone, neoaloesin A, 8-C-glucosyl-(S)- aloesol, 8-C-glucosyl-(2′-O-cinnamoyl)-7-O-methylaloediol A, isoaloeresin D and 8-Cglucosyl-7-O-methyl-(S)-aloesol, 8-C-glucosyl-7-O-methylaloediol, 8-C-glucosylnoreugenin	Anti-inflammatory	Hamman (2008)
Enzymes	Oxidase, alkaline phosphatase, amylase, bradykinase, carboxypeptidase, catalase, cellulase, lipase, and peroxidase	Reduces skin swelling, metabolism, and recycling of damaged tissue in the body itself	Verma (2016)
Inorganic Elements	Calcium, sodium, chlorine, zinc, iron, potassium, copper, magnesium	Teeth and bone formation, helps in maintaining healthy muscles, nervous system, immune system oxygen transport, nutrient delivery into body cells	Shahrezaee et al. (2018), Haque et al. (2014)
Miscellaneous including organic compounds and lipids	Potassium sorbate, arachidonic acid, γ-linolenic acid, triterpenoid, triglycerides, salicylic acid and uric acid	Anti-bacterial, essential fatty acid	Surjushe et al. (2008)
Amino acids	Alanine, arginine, aspartic acid, cysteine, glutamic acid, glycine, histidine, hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, serine, tyrosine and valine	Immunity, Regulates metabolic activities, Repairing and rebuilding of muscles	Surjushe et al. (2008)
Proteins	Lectins, lectin-like substance	Anti-bacterial and anti-septic	Verma (2016)
Saccharides	Mannose, glucose, l-rhamnose, aldopentose	Boosts immune system	Verma (2016)
Vitamins	Vitamin A, C, E, B1, B2, B6, B12, choline, folic acid, α-tocopherol	Antioxidants; cell communications; collagen synthesis; DNA synthesis	Surjushe et al. (2008), Hamman (2008), Verma (2016)
Sterol	Cholesterol, campesterol, β-sitosterol and lupeol	Improves skin barrier function	Surjushe et al. (2008)
Hormones	Auxins and gibberellins	Wound healing	Surjushe et al. (2008)

There are many reports focusing on the health benefits of the aloe vera, few of which are reported here. Kumar and Yadav (2014) have reported that consumption of aloe vera gel improved the blood and lymphatic circulation, kidney, liver and gall bladder functions, and digestion. The smooth functionating of colon, small intestines, and stomach is regulated by anti-inflammatory fatty acids present in aloe vera gel. These also helps in the recovery of epithelial tissues after injury and also, act as skin healer. Others benefits like a vigorous glow to skin after external use on skin, cures acne, laxative, antibacterial activity and antioxidant properties are delivered by aloe vera gel (Benzidia et al. 2018). The alcoholic extract of aloe vera gel at the concentration of 300 mg/kg showed decrease in blood glucose level in streptozotocin-induced diabetic rats. This showed that the antioxidant potential of aloe vera prevents formation of free radicals by various biochemical pathways and inhibiting the activity of enzymes by reducing glycation which results in decreased glucose level (Rjasekaran et al. 2005).

Rheological properties

The application of fresh aloe vera gel in several food product regimen has unsustainable reasons which relies on environmental as well as monetary factors. Hence to enhance its widespread deployment in food products, different processing technologies which can dramatically enhance functional properties and shelf stability of aloe vera gel have been explored (Swami Hulle et al. 2014). Recently, several approaches such as Freeze Drying (FD), Radiant Zone Drying, Refractance Window Drying (RWD), Spray Drying (SD), and High-Pressure Processing (HPP) have been extensively explored by researchers for preservation of aloe vera gel (Minjares-Fuentes et al. 2016; Nindo et al. 2010; Opazo-Navarrete et al. 2012). Nevertheless, these processing technologies utmost modify the original structure by inducing irreversible modifications to the groups of sugars/polysaccharide which may be associated with physicochemical and functional properties of aloe vera gel. Also, both the pulp and aloe gel contains a lot of insoluble polymer particles, which affect the rheological behaviour and physical stability mechanisms of the suspensions during storage and processing (Jorge et al. 2018).

Several authors have reported a non-Newtonian shear-thinning fluid behavior of aloe vera gel and stated that acetyl groups of acemannan polymer are involved in the shear-thinning rheological behavior of aloe vera (Campestrini, et al. 2013; Swami Hulle et al. 2014; Minjares-Fuentes et al. 2017). Thus, breakdown of this acemannan polymer induces Newtonian behavior of aloe vera gel (Nindo et al. 2010; Yaron 1993). Swami Hulle et al. (2014) observed that prolonged time interval between aloe vera juice extraction and its concentration before conversion to powder form changes rheological properties which could be due to further persistent enzyme activity and oxidization that dramatically causes product disentanglement and deterioration. Therefore, it is necessary for researchers to understand the flow behavior, viscosity and viscoelastic properties of aloe vera gel during processing.

The flow behaviour and viscosity

The food processing can lead to considerable alteration in temperature during food product formulation which changes the rheological parameters of the aloe vera juice and thus, its correlation with temperature effect is of great importance. Power law model of aloe vera gel flow behaviour index (n) values ranged from 0.48 to 0.55 (at 10 to 50 °C) indicates a shear-thinning behaviour (Minjares-Fuentes et al. 2016). The structural arrangement caused by hydrophobic interactions, acetylation pattern of the acemannan polymer in the development of polysaccharidic hydrogel structure obeys shear-thinning flow behaviour of aloe vera (Campestrini et al. 2013; Lad and Murthy 2013). Shear-thinning behaviour results when a serious imbalance of molecules occur which can effectively lower the resistance of flow at increasing shear rate. Most probably food samples containing numerous ingredients for instance pectic and plant tissue molecules imbedded in solution/dispersion interact with each other at a certain degree and dramatically display a nonlinear behaviour (Steffe 1996). The viscosity of the fresh aloe vera sample was clearly dependent on shear rate values for temperatures ranging between 10 and 50 °C indicating a pseudoplastic shear-thinning behaviour. Whereas, the shear stress value of reconstituted aloe vera gel samples dried using Spray Drying, Freeze Drying, Refractance Window Drying, Radiant Zone Drying was independent on shear rate values which show Newtonian flow behaviour (Minjares-Fuentes et al. 2016; Nindo et al. 2010).

Yaron (1993) reported the Newtonian flow behaviour of the aloe vera mucilage when stored at room temperature or at 40 °C for 48 h. Swami Hulle et al. (2014) observed a considerable change in viscosity of aloe vera gel when temperature rises from 10 to 50 °C. This could imply the macromolecule mobility induced due to rise of temperature which further improves the flow and reduces the viscosity. Kiran and Rao (2014) investigated the effect of drying methods on aloe vera and observed the rheological characteristics of these powders after reconstitution. The outcomes clearly recommended that the viscosity of FD samples was at utmost level as compared to other selected methods. The impact of FD technique was least to the polysaccharide content of aloe vera gel and the morphology of pectinaceous substances present in aloe vera gel was well preserved which dramatically improved the rheology of gel.

HPP is novel technology which is being explored rigorously by researches from last few years for food processing applications. Several authors opted out HPP of aloe vera juice, gel or suspensions and studied its rheological parameters for its utilization in food industry. HPP treated aloe vera samples exhibited a non-Newtonian shear-thinning behaviour. The flow behaviour index (n) for HPP treated aloe vera suspensions ranged between 0.16 and 0.25 which indicates a shear-thinning behaviour moreover it can be also implied that the behaviour is beyond Newtonian characteristic. The pressure treatment of aloe vera juice reduced its flow behaviour index concomitantly. Besides, soluble solids content improved with the pressure treatment (Swami Hulle et al. 2014). The distribution of macro and micro ingredients affects the flow behaviour index, probably the HPP have greater impact on the particles such as soluble solids and presence of different functional groups (–CH, =CO, –OH, –CH3 and –COC) are intended to reduce flow behaviour index during HPP of aloe vera. Moreover, a decrease in apparent viscosity (Pa s) with shear rate was observed in HPP treated aloe vera samples (Opazo-Navarrete et al. 2012). The consistency coefficient (k) was increased at 300 MPa and 400 MPa for 1 min treated aloe vera samples which was resulted from improved interaction of pectic molecules (Opazo-Navarrete et al. 2012).

The influence of water deficit on the rheological properties of aloe vera mucilage has been studied by Minjares-Fuentes et al. (2017). Non-Newtonian (shear thinning) comportment was detected in fresh and reformed aloe vera mucilage. However, Newtonian plateau at higher shear rates was exhibited only in fresh aloe vera mucilage signifying disentanglement of long chain polysaccharide at greater shear rate. An analogous behaviour was witnessed in aloe vera juice and gel by Lad and Murthy (2013). There was an increase in the flow behaviour index (n) recorded from 0.47 to 0.57 for re-formed aloe vera mucilage when water insufficiency was reduced from 60 to 0% respectively (Table 2). The volume and type of water-soluble polysaccharides greatly influenced the flow behaviour of reformed solutions. The rise in the viscosity of aloe vera mucilage can be related directly with the reduction of mannose residues from acemannan. Perhaps, increased pseudoplasticity parameter (n) may be due to the increase in regular molecular weight of the bioactive acemannan polymer as a result of water insufficiency (Minjares-Fuentes et al. 2017).

Table 2.

Flow behaviour index of aloe-vera samples

Sample (solid content)	Temperature (C)/water deficit (D %)/pressure (MPa)	Flow behaviour index (n)	Instrument type/geometry	Inference	References
Aloe vera juice (1.5°Brix)	15 °C 25 °C 35 °C 45 °C 55 °C	0.710 0.627 0.685 0.717 0.809	Stress-controlled dynamic rheometer (Bohlin Gemini 200, Malvern Instruments Ltd, Malvern, U.K.) and coaxial cylinder (C25—cup and bob) geometry Rheological model Ostwald–de Waele (or power law) used for analysis of flow characteristics analysis	Non-Newtonian shear thinning behaviour Decrease in n value with increase in solid content of juice Increase in the pseudoplasticity of aloe-vera juice concentrates Considerable drop in n values with increase in temperature attributed to greater H-bond formation favoured owing to higher concentration	Swami Hulle et al. (2014)
Aloe vera juice (2.5°Brix)	15 °C 25 °C 35 °C 45 °C 55 °C	0.366 0.404 0.434 0.469 0.473
Aloe vera juice (3.5°Brix)	15 °C 25 °C 35 °C 45 °C 55 °C	0.409 0.371 0.451 0.407 0.432
Aloe vera juice (4.5°Brix)	15 °C 25 °C 35 °C 45 °C 55 °C	0.343 0.399 0.447 0.389 0.428
Aloe vera juice (5.5°Brix)	15 °C 25 °C 35 °C 45 °C 55 °C	0.265 0.276 0.330 0.345 0.347
Aloe vera mucilage reconstituted (~ 1.0–1.5% w/v)	D0 D40 D60	0.57 0.52 0.47	Stress-controlled rheometer (Model AR-G2, TA Instruments, New Castle, Delaware, USA) with double-concentric cylinder geometry (21.96 mm and 20.38 mm were the measurements of the outer and inner cylinder diameters, respectively, 59.50 mm height, and 500 μm gap)	Fresh aloe vera mucilage’s exhibited a Newtonian plateau at high shear rates Reconstituted aloe vera mucilage’s depicted non-Newtonian Shear-thinning behaviour The Ostwald-de Waele model describes the flow behaviour of the reconstituted mucilage’s. Increase in the pseudoplasticity (n) with decrease in water deficit could be due increase in the average MW of the bioactive acemannan polymer	Minjares-Fuentes et al. (2017)
Aloe vera suspension HP treatment (1 min)	0.101 MPa 300 MPa 400 MPa 500 MPa	0.23 0.16 0.17 0.25	Physica MCR 300 (Anton Paar, Germany) and the instrument was fitted with parallel plate (50 mm diameter; smooth) geometry	Herschel–Bulkley model depicted Shear-thinning behaviour This value indicates that the behaviour is far from Newtonian character Particular for foods containing bulk of dispersed particles which are accountable for the response between the applied strain and contrary effort to nonlinear flow	Opazo-Navarrete et al. (2012)
Aloe vera suspension HP treatment (3 min)	300 MPa 400 MPa 500 MPa	0.17 0.20 0.23
Aloe vera suspension HP treatment (5 min)	300 MPa 400 MPa 500 MPa	0.18 0.23 0.20

Viscoelastic properties

Viscoelastic properties control the texture of foods/food ingredients specifically those which show both elastic as well as viscous behaviour. Viscoelastic properties G’ and G”, storage and loss modulus, respectively, as a function of frequency are mostly measured by using oscillatory rheological experiment which is also referred as oscillatory mechanical spectroscopy (Barnes 2001). Polysaccharide solutions seems like a viscoelastic substance which can illustrate liquid and solid characteristics at the same time. The G’ and G” modulus denote the elastic and viscous behaviour of the sample (Bourbon et al. 2010). A strong predominance of the viscous modulus (G″ > G′) at a frequency range of 1–100 rad/s was detected in the oscillation sweep test for fresh aloe vera mucilage (Minjares-Fuentes et al. 2017) just like a solid behaviour as reported earlier by Medina-Torres et al. (2016) considering fresh aloe vera. This could be either due to the structural configuration of the acemannan polymer or the potential interaction between acemannan and cell wall polysaccharides (e.g., pectic substances). Strangely, the sample of fresh mucilage without water deficit depicted greater modulus (G″, G′) than 40% and 60% water deficit sample. Moreover, at lower frequencies, it showed independent frequency region. The reason for this may be because of high volume of water preserved by acemannan polysaccharides retained in the Aloe vera samples. Furthermore, there was a similarity found between the elastic modulus and the vicious modulus of the reformed mucilage, while a crossover point at 7.39 rad/s was depicted in the sample with 40% water deficit (Minjares-Fuentes et al. 2017). A comparable viscoelastic behaviour have been observed in reformed aloe vera mucilage by few researchers, wherein they found that the reformed mucilage solutions with up to 6% high solid content displayed excellent gelling properties at crossover point when the frequency was set at a lower range (Campestrini et al. 2013; Medina-Torres et al. 2016). In addition, Ross-Murphy (1995) linked crossover between G’ and G” to weak gels. Some researchers recommended that crossover point can be used as an indicator to depict viscoelastic behaviour of material which depend upon the water-soluble polysaccharides (Campestrini et al. 2013; Lad and Murthy 2013; Swami Hulle et al. 2014).

However irrespective of the HPP treatment time, aloe vera reduced the viscoelastic parameters of the elastic modulus (G′) at 300 MPa for 1 and 5 min and at 400 MPa, at the same time the greatest modulus (G′) was observed for the untreated samples. Beside the reduced viscous modulus (G″) values were observed for samples treated at 300 MPa for 1 and 5 min, at 400 MPa and at 500 MPa for 1 min. Hence, HPP treatment is a good choice for effectively modulating the rheological parameters such G′ and G″ of aloe vera gel. Despite storage of aloe vera suspensions at 4 °C displayed a weak gel-like behaviour with G′ > G″, the elastic behaviour of Aloe vera suspension represent a greater impact than viscous behaviour during storage (Opazo-Navarrete et al. 2012).

Application of aloe vera in foods

Aloe vera gel has excellent medicinal, functional and nutritional properties and its incorporation into food can increase its medicinal, functional and nutritional value (Jayabalan 2013). Saccù et al. (2001) have identified mmore than 70 aromatic compounds in the aloe vera using headspace GCMS and RP HPLC. Majorly present aromatics are alcohols, organic acids, aldehydes, triglycerides, enzymes, potassium sorbate. Researchers have explored the application of aloe vera juice in different food products such as bakery, confectionary, beverages and dairy where it can act as a bio-preservative as well as improves the quality parameters of food products. Aloe vera is also been used as a food supplement. The following section elaborates on the application of aloe vera in different food sectors.

Preservative

Shahrezaee et al. (2018) explored the use of aloe vera gel powder (AGP) for extending the shelf life of partially cooked chicken nugget and cold stored chicken nuggets. AGP helps in the reduction of microbial load by extending shelf life of both partially cooked chicken nugget and cold stored chicken nugget up-to 6 days at refrigeration temperature. Das et al. (2011) identified 14 kDa protein in AGP which showed the potential against the growth of yeast. Also, the organic acids like succinic and citric, acid, present in AGP which lowered pH and resulted in the inactivation of microbial activity (Bozzi et al. 2007). Author suggested to use refrigeration system instead of freezer which enhanced shelf life effectively by two weeks with the concentration of 2.5% and 3.5% AGP in chicken nugget. AGP also improved the textural qualities like gumminess, chewiness, cohesiveness, hardness, and springiness (Shahrezaee et al. 2018). AGP also softened the chicken nugget due to presence of polysaccharides such as acemannan, glucomannan, and cellulose which contributes a structure of gel formation and inhibit binding of protein/myofibrils interaction (Umano et al. 1999). Hence, AGP contributing as bio-preservative with improvement in textural quality parameters in meat-based products.

Appropriate relative humidity (RH) is important to control decay development and water loss from fruits and vegetables. Therefore, high RH values are usually employed to preserve fruits and vegetables during post-harvest storage moreover developed films could suffer fractures at low ambient RH due to their glassy state. Hence, under conditions slightly above the critical moisture contents and the critical water activities coating materials will be neither brittle nor so sticky and this can be achieved via incorporation of aloe vera. The starch-based antifungal edible films developed by Ortega-Toro et al. (2017) by incorporating aloe vera into starch matrices in the ratio of 1:1, using glycerol as plasticizer which effectively control growth of fungus and moisture loss in cherry tomatoes. Synthetic fungicides used in the preservation of fruits and vegetable can be replaced with aloe vera due to its non-toxic nature and serve as natural source of preservatives. Similarly, fresh harvested plum and peaches coated with either Aloe arborescens gels or Aloe vera showed delay in ethylene production during the ripening at 20 °C for six days (Guillén et al. 2013). The 0.5% of aloe vera coating on the eggplant controlled and delayed in the non-reducing sugar, pH, moisture loss, total sugar, and shriveling with minimizing the losses of vitamin C (Amanullah et al. 2016). Aloe vera has also extend shelf life of freshly cut fruits. Sepulcre et al. (2015) compared the efficacy of aloe vera, sodium alginate and citosan based coatings for imcreasing the shelf life of kiwi fruit slices by maintaining firmness along with prevention of ascorbic acid and yellowing which occurs due to ripening. Even in the case of sensory analysis aloe vera treated kiwifruit slice was preferred more by sensory panel. Hence, aloe vera play crucial role to extend postharvest shelf life by maintaining sensory properties for about 12 days of the storage. Thus, it can be concluded that aloe vera can be used as potential bio-preservative in different food products including processed food as well as fresh produce with proven antioxidant and antimicrobial properties (Shahrezaee et al. 2018).

Food supplements

The concentrated nutrients with nutritional and physiological effect, which lack in the normal diet are provided through food supplements. The attention of food industry towards aloe vera products is mainly due to its medicinal benefits which encourages to utilize the extract as supplements in the preparation of functional foods (López et al. 2017). In the recent years, aloe vera in the form of highly concentrated powders have been employed for the same purpose. Various other forms such as Whole Leaf Powder (WLP-decolorized), Inner Leaf Powder (ILG-decolorized) can also be used for supplementing food products which are produced using spray drying processing. Aloe vera is also been used in the cube forms (Swami Hulle and Rao 2016). Authors have carried comparative assessment by using high pressure processing (300-500 MPa for 5–15 min) and dehydration processing (50–70 °C and air velocity of 1–2 m/s) on cubes of aloe vera. They observed that texture of cubes gets improved by HPP with enhancing moisture transfer rates in aloe vera which could be used as food supplements.

Bakery

Aloe vera has shown different applications in bakery products. It can act as a hydrocolloid which can modify the rheology and texture properties of food products. Ghiasi-esfahani (2015) formulated low meat burger using texturized soy protein and aloe vera. The addition of aloe vera in meat burgers enhanced it quality like by reducing cooking shrinkage, lipid oxidation, cooking loss, and fat absorption. The textural qualities along with moisture retention improved in low fat burger by addition of aloe vera. These properties are important for production of a good quality low meat beef burgers and they also lead to the diameter reduction in the burgers.

Aloe vera gel (AG) is rich in cellulose and pectic substances which are used as fat replacers in food industries. Chopra (2017) have reported the use of AG as a fat replacer in the preparation of cakes (low fat cream) especially for people who are overweight and obese. They have found that fat replacement by aloe vera gel in cakes is a potential intervention aimed at maintaining and/or reducing body weight among overweight and obese individuals along with intake of valuable nutrients of AG.

Aloe vera fortification improved rheological characteristic of Barbari dough with improved bread quality and shelf life. Dough water absorption and dough development time increased with all concentration of aloe vera powder. Addition of aloe vera powder (9%) to dough formulation was more effective in terms of reduction in dough extensibility. Therefore the addition of aloe vera, is a suitable for extending the shelf life of the bread (Jafari et al. 2018). Hence, utilization of aloe vera in the preparation of meat burger, bread and cakes shows that improvement in textural qualities which indicates that suitability as hydrocolloids.

Beverages

The nutraceutical potential of aloe vera gel explored as functional ingredient in the preparation of various health based food products such as yogurts and beverages (Swami Hulle et al. 2014; Bornare 2015). Aloe Vera based beverages have shown potential to serve as a health/functional food product and hence their availability in the market will definitely benefit the health conscious people (Sharma et al. 2015). Though the pure aloe vera juice has good nutritional, antioxidant and antimicrobial properties, the sensory characteristics are not very acceptable. The formulation of soft drink based on aloe vera juice and gel are better option for more nutritious and health based soft drinks (Talib 2016). Bornare (2015) have standardized and developed ready-to-serve (RTS) mango beverage with different blending proportions of aloe vera. The aloe vera juice (10%) incorporated with the blend of mango pulp, sugar, and citric acid helped in improving the organoleptic quality (taste) as well as quality of beverages. Above 20% addition of aloe vera juice, the organoleptic properties were not acceptable due to the bitterness imparted by aloe vera juice. In addition to that physicochemical and nutritional qualities of final products were also improved with storage ability for 3 months without affecting organoleptic and chemical qualities.

Swami Hulle et al. (2017) has designed the experiments to understand the effect of thermal processing (TP) and high-pressure processing (HPP) on storage of mixed beverages of aloe vera-litchi. Authors found that HPP was more effective in the keeping the beverage fresh as compare to TP. HPP also increased the shelf life for about 100 days at 4 °C even the sensory attributes were unaffected till then and also concluded 60 °C for HPP technology effective for keeping a stable shelf life for fruit based beverages. Contreras-Lozano et al. (2018) developed the aloe vera based sweet corn juice. Authors have studied the flowability and stability of the blended juice and found that flowability changed from shear thickening to shear thinning with increased stabilty of the juice. Trivedi et al. (2012) attempted to develop a herbal wine from aloe vera. They found to have the similar composition and sensory qualities with respect to traditional grape wine. Along with that, bactericidal activity exhibited by herbal wine against food borne pathogens like Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium.

Confectionary

Different confectionary products such as jelly, chocolate, jams, marmalade and ice-creams fortified with aloe vera as functional and nutritional ingredient. Palve et al. (2015) explored the addition of aloe vera gel and pineapple juice in jelly preparation which was prepared by boiling from filtered fiber free extract with addition of sugar, citric acid and pectin. They have found that blending of aloe vera and pineapple in jelly formation is good option to improve aloe vera utilization. Jayabalan and Karthikeyan (2012) attempted to use the application of aloe vera in chocolate preparation. The ingredients like skimmed milk powder, cocoa powder, sugar, and aloe vera juice are combined to create completely different taste and texture sensations. They employed response surface design for optimization of formulation which provide formulation of sugar (1022 g kg⁻¹), citric acid (28.2 ml kg⁻¹), aloe vera juice (990 ml/kg), and pectin (50.3 g kg⁻¹) for the preparation of jam on the basis of sensory score (Jayabalan 2013). Marmalade is another jelly like product made usually from citrus fruit juice and peel with sugar. Orange marmalade were prepared with incorporation of aloe vera powder which shows significant changes in sensory and physicochemical properties of marmalade (Rashid et al. 2014). They observed protein, titratable acidity, and fibre contents increases as concentration of aloe vera powder increase in orange marmalade by decreasing fat contents. The alarming situation for dairy products is diabetic patients increases in India, which demand for natural and functional ingredients. Ice cream is one of the oldest fat rich medicines. Manoharan et al. (2012) reported that maximum 20% of aloe vera juice utilized in the ice cream preparation without affecting organoleptic properties of ice cream. The aloe vera gel concentrate, aloe vera cubes, aloe vera gel powder, and sugar coated aloe vera cubes were utilized as functional ingredient in the preparation of ice-cream (Khatkar et al. 2014). Thus, it can be concluded that aloe vera can be potentially used as a formula for further development at commercial scale.

Dairy

Aloe vera is used in different dairy products such as yogurt, buttermilk etc. due to its highest therapeutic values. The yogurt with aloe vera gel is a good source for supplying bioactives in a palatable form. Govindammal et al. (2017) attempted to formulate the aloe vera fortified yogurt. When compared with the control, aloe vera fortified yogurt showed lower fat content and high in fiber and phytonutrients such as steroids, phlobatannin, saponins, and anthraquinones. Authors Throughout concluded that aloe vera gel fortified yoghurt found superior and also found to be good probiotic along with good taste, which could essentially transfer to the consumer. A dairy beverage i.e. buttermilk has proven high therapeutic and nutritive benefits. Khatkar et al. (2014) fortified aloe vera juice, in buttermilk which increased viscosity (depends on addition of aloe vera juice) with enhancement in physicochemical, nutritive and sensory characteristics. This showed improvement in dietary fiber, vitamin C, and iron after fortification of aloe vera juice in buttermilk.

Safety aspects of aloe vera

Aloe vera based cosmetic and food products gained popularity as natural products, where it is utilize as ingradient. As such there is no adverse effects of aloe vera observed on the health, but if it is contaminated with anthraquinones may show the symptoms like discomfort, irritation, and slight itching (Bradshaw 1996). Aloe vera is costly product, so it is adultered with water to gain buisness profits. As such there is no consumer parameters set by food regulations bodies and agency, which must be on priority. The certain components like emodin and anthraquinones are found at low level. It shows toxicity in higher concentration or daily exposure to aloe extracts. Thus, there is a need to develop rapid bichemical analysis tools for the application of aloe vera in food products (Shukla et al. 2017; Javed and Rahman 2014).

Future perspective and conclusion

The application of aloe vera in medicines has witnessed its long tradition in human wellness. Recent studies have confirmed that aloe vera has a potential to be used in the food application where its rheological behaviour plays important role. It contains various bioactives which can be utilized for the functional food preparation or as a nutraceutical. Thus, due to its the functional properties, aloe vera can be boom to the food industries. Aloe vera is still unexplored for its food application especially in cereals, beverages sectors. There are very limited studies on its application in different food sectors such as dairy, confectionary, bakery etc. This review gives insight on chemical composition, health benefits, rheology, flow behaviour index, and viscoelastic properties of the aloe vera which determines the utilization of aloe vera in food applications. There are very few studies on the application of aloe vera as bio-preservative especially in nonvegetarian products. Also, which bioactive component of aloe vera interact with food product for increasing shelf life need to be find out, and it could also be future aspects to check its preservative effects other category of food aspects of cereals and beverages. A wide range of food processing techniques and food products should be developed using aloe vera juice and mucilage. Therefore, the need of the hour is to explore the aloe vera by researchers with the aim to achieve food and nutritional security.