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. 2020 Nov 4;58(11):4127–4138. doi: 10.1007/s13197-020-04877-6

Effect of inulin and date syrup from Kaluteh variety on the qualitative and microbial properties of prebiotic ketchup

Davood Mirzaei 1, Ahmad Pedram Nia 1,✉, Mahdi Jalali 1
PMCID: PMC8405754  PMID: 34538897

Abstract

The physicochemical, sensorial, and microbial properties related to the samples of ketchup containing different inulin (0, 3.75, and 7.5%) and date syrup values (0, 2.25, and 4.5%) were assessed in the present study and the results were analysed through statistical response surface method. Considering the mutual effect, an increase in inulin level led to a primary upward and secondary downward trend in brix and synersis, while the conditions were reversed by enhancing date syrup one. In addition, the mutual effect of inulin and date syrup on sensorial properties represented that flavour and overall acceptance first increased by improving inulin amount and decreased in the following, which was different to colour parameter, while adding date syrup affected colour factor in produced ketchup appropriately. Further, an enhancement in inulin value influenced a little the presence of acid-resistant bacteria, yeast, and mould, while increasing date syrup one led to the durability of microbial corruption. Finally, using the optimum levels of inulin (3.75%) and date syrup (1.13%) could affect ketchup formula properly.

Keywords: Ketchup, Inulin, Date syrup, Prebiotics

Introduction

Ketchup is nutritionally considered as a source of valuable carotenoids such as lycopene, and improving the nutrition fact of which through new formulation is regarded as essential for consumer health due to an increase in using ready meal and ketchup (Mert 2012). The level of these materials in foods is decreasing by considering the increase in consumers' awareness and the relationship between the prevalence of chronic diseases such as obesity, cardiovascular diseases, and type 2 diabetes with an increase in macromolecules such as sugar and fat in diet (McClements and Demetriades 1998). Functional foods are defined as the food materials possessing the impacts beyond of their nutrition fact or content on human health. The functional foods can be divided into probiotic, and symbiotic groups. The compounds such as plant fibres, known as dietary fibres, are commonly used in order to produce low-calorie foods. Dietary fibres, as a subset of prebiotic carbohydrates, fail to decompose by the enzymes of human digestive system and ferment by colon microbial flora. Nutritionists expressed different health benefits for dietary fibres, including decreasing blood serum cholesterol and blood sugar levels, preventing cancer, constipation, appendicitis, and consequently avoiding diabetes and obesity (Wang 2009).

Inulin is considered as one of prebiotics, which is laid in dietary fibre class. It is regarded as a linear polysaccharide β (2 → 1) fructosyl bonds and a glucose molecule at the end of each chain, and its physicochemical properties depend on the degree of polymerization (DP) (2–60 units). Since an increase in the chain length and DP of inulin results in reducing solubility level and hydration intensity, long-chain types possess less solubility and more viscosity and are used as texture consisting and improving agent (Tárrega et al. 2010). Based on the previous studies, adding pectin, inulin, and β-glucan possesses no negative effect on some of the physicochemical, textural, and sensorial properties of low-fat mustard sauce with carbohydrate-based dietary fibres as fat alternative (Hosseinvand and Sohrabvandi 2016). Adding inulin dietary fiber plays an effective role in maintaining phenolic compounds and performance of ketchup antioxidants in human body (Tomas et al. 2018).

The sucrose extracted often from sugar beet or saccharum is abundantly applied in food products and its high consumption is higher than the amount of its global production. Accordingly, some studies were conducted to find another source for producing sucrose except sugar beet and saccharum. The alternative sources should possess no adverse effects on human health and product quality and be affordable. The date is considered as a sugar-enriched fruit (42–88%), which can be utilized as a fresh sugar source. Date fruit contains different minerals, especially phosphorous, copper, magnesium, potassium, and a significant value of calcium, vitamins, and phytochemical compounds, along with sucrose and possesses health and anticancer impacts (Al-Farsi et al. 2006). Due to the limitation of foods, especially sugar-containing ones, many researchers highlight their optimum use such as utilizing food wastes todays. The date syrup is produced from second- and third-grade dates in date processing plants and can compete with its similar products such as beehive honey. Additionally, it is applied directly or in the formulation of some foods such as some bakery products, beverages, confectionaries or a combination of sesame paste and date syrup (Razavi et al. 2007). Date pulp was added into the formulation of ketchup in order to maintain tomato sustainability, along with improving nutrition fact, leading to positive outcomes (Nasir et al. 2014). Thus, the present study evaluated the effect of adding inulin and date syrup as alternative prebiotic and sugar rich sources on the qualitative and microbial properties of ketchup.

Materials and methods

Materials

In this study, inulin was utilized according to the product of long chain type (22–25 units) (AdonisGol Darou Co., Iran), which are industrially produced from ordinary inulin, because by reducing the intensity of hydration, the amount of solubility and viscosity increases and can be a good thickening agent, date (Kaluteh variety) Kerman, Iran (ash 1.84%, total sugar 74.76%, protein 2.311%, sucrose 5.03% and total phenolic compounds 720 mg gallic acid per 100 g dry weight of sample and color Blackish brown), 30 brix tomato paste (FaFa food industries, Iran), distilled vinegar (Amin Trading Co., SEPTICO, Iran), xanthan gum (Sigma Aldrich, USA), liquid glucose (Iran Dextrose Co.), white sugar, sodium chloride, flavouring, wheat refined starch (food ingredient supplier store), and other chemicals (Merck, German).

Extracting date syrup

The experiments were conducted in two steps. In order to obtain the maximum sugar extract from date, the intended value of date was first taken out of cold storage and placed in laboratory until reaching ambient temperature because of firming its texture within cold storage and failing to homogenise and diffuse well during stirring by manual mixer. In addition, dates were manually sliced into smaller pieces and mixed with 500 gr of the distilled water reached to laboratory temperature through water bath (type W350B) with 1:4 ratio in order to increase water-date interface and accelerate diffusion process. Further, it was hemogenised by using manual mixer with low speed for 2 min for further extraction of its sugar syrup and its pH was regulated at 4 by utilizing 5 N citric acid and 1 N sodium hydroxide. Furthermore, sample-containing beaker was transferred into a 77 °C water bath, kept for 5 h at intended temperature, and cooled up to ambient temperature by cold water. Finally, cooled solution was filtered by using fabric filters (Abbès et al. 2011).

Preparing inulin

To form the gel, 90% (w/w) inulin was mixed with 10% (w/w) water and then stirred at 80 °C for 10 min and finally cooled to 25 °C (Hosseinvand and Sohrabvandi 2016).

Preparing ketchup

In this regard, 20% of tomato paste (30 brix), 11.5% of white sugar, 2% of sodium chloride, 7.5% of distilled vinegar, 5% of glucose syrup, 4% of wheat refined starch, 0.2% of xanthan gum, 0.4% of different spices (flavouring, and onion and garlic powder), and 49.4% of drinking water was applied to make tomato ketchup based on 20% (w/w) tomato paste. Regarding control ketchup, tomato paste was first poured into the total water existing in the formula, all materials existing in the formula expect sugar, vinegar, and glucose syrup were added, stirred, and heated up to 75 °C for 15 min. Then, sugar, vinegar, and glucose syrup were mixed, heated to 55 °C, and poured into the mixture. Finally, the temperature increased to 88 °C, product was heated for 5 min, and hot tomato paste was packed. Before producing the samples of ketchup with the variables of inulin (0, 3.75, and 7.5%) and date syrup value (0, 2.25, and 4.5%), the prepared inulin suspension was mixed with tomato paste, sodium chloride, starch, xanthan, and spices were poured, and heated at 75 °C for 15 min. In addition, the mixture of hot sugar syrup, glucose syrup, and vinegar was added, heated at 88 °C for 5 min, and filled as hot into 200 ml PET dishes. All steps of stirring and heating the samples of ketchup were conducted by using a 600 Vorwerk electrical thermomix (Canada).

Physicochemical tests of ketchup

The pH and brix related to the sample of produced ketchup were measured based on the AOAC standard (2005). In order to assess the synersis percentage of ketchup, the samples were centrifuged by using Sigma 3 K centrifuge (German) at 4700 g for 20 min after passing three months of producing and storing in the refrigerator. Additionally, 10 gr of each sample was weighted and centrifuged, and released serum was separated. Further, precipitate was again weighted and synersis percentage was determined through following formula (Şahin and Özdemir 2007).

Synersis=primarysampleweight-secondarysampleweightprimaryweight×100 1

Sensorial test of ketchup

The samples were coded by using the random codes consisting of two letters and two numbers and provided to taste judges in colourless dishes. Additionally, taste judges were asked to evaluate the samples with respect to color, taste, texture and overall acceptance or pleasureness, and the minimum and maximum scores for each sensorial property were denoted by 1 and 5, respectively (Liu et al. 2007).

Microbial test of ketchup

In order to probe acid-resistant bacteria by observing sterile conditions, 4 ml of 0.1 dilution was transferred into four sterile plates. After reaching about 40 °C, 15 ml of the agar growth medium containing orange extract was added into two plates, while APT growth medium was used in others. Further, the medium and sample were mixed and placed on a flat and cool surface until solidifying. Furthermore, the plates were incubated at 30 °C for 5 days and then evaluated with respect to the presence of acid-resistant bacteria (AOAC 2012). The growth medium used for DRBC, which prevents bacteria from growing and allows only yeast and mould to grow, was applied to assess the growth of moulds and yeasts. The growth medium was prepared based on their preparation method, 1 ml of diluted sample (0.1 dilution) was poured into empty plate, and growth medium was added and solidified. Then, the plate was placed at 25 °C for 4–5 days and investigated with respect to the presence of mould and yeast after incubation period (AOAC 2012).

Statistical Analysis

Response surface methodology (RSM) was used in the present study to find the effect of the independent variables of inulin and date syrup in order to determine optimum conditions. The data obtained in the design were modelled by using Design-Expert software and three-dimensional response surface curves were drawn to assess the relationship between responses and independent variables. In addition, the numerical optimization method in the software was applied to specify optimum point. For this purpose, a central composite design with three levels and three repetitions at the central point was used to investigate the effect of date syrup and inulin for the production of ketchup sauce (+ 1, 0, − 1) (Table 1). Response functions (y) include physicochemical and sensorial properties, which quadratic polynomial model was fitted on the data obtained from experiments. The coefficients of quadratic model, which represent the effect of using the raw materials of inulin and date syrup on the physicochemical, sensorial, and microbial properties of tomato ketchup as the product, were calculated through least squares method and provided as the equation of experimental models.

Table 1.

Independent variables and their application level for optimizing ketchup sauce

Independent variables Variables level
− 1 0  + 1
Inulin (%) (A) 0 3.75 7.5
Date syrup (%) (B) 0 2.25 4.5
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Results and discussion

Mutual effect of variables on pH

Figure 1 displays the response surface curve related to the effect of the variables of inulin and date syrup on the pH of ketchup. In the polynomial model (Eq. (2)), the R2 and adjusted R2 were 0.9527 and 0.9190, respectively, which indicate a good description of the data scatter. Also, the non-significance of non-fit factor at 95% confidence level had the best fit on pH response data. Since the prebiotic compound used in the formulation of food product should be sustainable during processing, galactooligosaccharides and long-chain inulin can be utilized in products such as the ketchup which possesses low pH (≤4) and is pasteurized at high temperature (around 90 °C) (Mansouripour et al. 2017). Regarding the effect of applying β-glucan on mayonnaise, using different levels of β-glucan failed to affect the pH of samples (Worrasinchai et al. 2006).

Fig. 1.

Fig. 1

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Response surface curves for pH, brix, and synersis, and specifying the effectiveness of independent variables

As shown in the response surface curve in Fig. 1, the linear (p < 0.0001) and square effects (p < 0.05) related to the variable of date syrup can have a significant effect on the pH in the desired range, because the pH of different formulations varied between 3.69–3.74, all of which were within the allowable standard range (maximum 4). The reason for this significant effect of pH by increasing the percentage of replacing inulin and date syrup can be related to the decrease in hydrogen ion concentration due to the effect or increase in the aqueous phase (Majzoobi et al. 2016). Amini et al. (2019) sought to replace high-fructose corn syrup with sucrose in ketchup and obtained the pH of samples as 3.49–3.69 by indicating no significant effect of the value of high-fructose corn syrup on the changes in pH. The results of ANOVA demonstrated the insignificant effect of inulin and date syrup in ketchup (p > 0.05), leading to a gentle increase in pH parameter up to 3.75 due to the adjuster effect of inulin. El-Sharnouby et al. (2009) obtained 890 gr of date syrup with 18.8% moisture, 75.5° brix, and pH 4.12 from 1 kg date pulp, which could help formulated ketchup to sustain to microorganisms due to its high acidity.

pH=+3.55-0.003A+0.009B-0.014AB+0.015A2+0.020B2 2

Mutual effect of variables on soluble solids content (brix)

The effect of the independent variables including inulin and date syrup on the changes in the brix of ketchup is presented in the response surface curves in Fig. 1. Appropriate correlation coefficient (R2 = 0.9186) confirms the fit of 96.18% of the total changes in the range of values studied by the regression model. The R2 and adjusted R2 values were 0.9618 and 0.9228, respectively, which indicate a good description of the data scatter. The suitability of the model was evaluated using the lack of fit test, which was not significant for (p > 0.05) (Eq. (3)). Based on the results of ANOVA in brix data, the linear (p < 0.0001) and square effects (p < 0.05) of inulin was significant in the model. Thus, brix value first increased and then decreased by enhancing inulin value from 0 to 7.5%. The regression coefficients obtained from Eq. (3) represented the negative effect of improving inulin on the brix of ketchup. These results are inconsistent with those of Juszczak et al. (2013) who reported no significant difference in the brix related to the samples of ketchup by adding inulin and galactooligosaccharide in order to reduce sugar level. The square effect (p < 0.01) was the only significant effect for date syrup. The results demonstrated that an enhancement of date syrup value in ketchup resulted in increasing brix parameter due to the presence of higher brix. Degree brix improved in the product by considering the percentage of the weight of solids content existing in a solution to the total weight of solution or weight percentage of solids content in a solution and date syrup contains high soluble solids content (Jalali et al. 2014; Fawzia et al. 2000). Assessing the mutual effect of inulin and date syrup represented that improving inulin content led to a primary enhancement in degree brix and secondary reduction, while it firstly decreased and then increased by adding date syrup, and optimum value was obtained as 3.38. Date syrup is a thin or thick liquid, which takes out by pressing or solving in water or diffusing date. In addition, it contains all soluble ingredients existing in date, possesses more concentration and brix over than 50, and can positively affect the brix of final product. Date syrup is highly used since its long-term maintenance faces with sugar spotting problem at high brix and the problem of microbial corruption at low brix (Abbès et al. 2011).

Brix=+25.25+1.510A+0.190B+0AB-2.150A2+1.310B2 3

Assessing the effect of independent variables on synersis percentage

Figure 1 illustrates the effect related to the independent variables of inulin and date syrup on the variations in the synersis percentage of ketchup as response surface curves. The square effects related to the variable of date syrup for the synersis value of produced ketchup were significant based on the results of ANOVA. The insignificant effect related to the variable of the inulin applied in ketchup (p > 0.05) indicated the insensitivity of ketchup to the changes in inulin values. Accordingly, synersis percentage varied insignificantly by changing the values of this variable.

In the present study, 4% of wheat starch was used to prepare ketchup sauce in the formulation of the samples. Regarding the results of the synersis percentage, samples with inulin and starch had more synersis due to the negative synergy between the two compounds. This negative synergy is due to the greater tendency of inulin to water compared to starch, the presence of polymers in concentrations below 20% and the action of inulin as a diluent. Since inulin has a higher affinity for water than starch, more water binds to the inulin chains and the viscosity decreases (Mansouripour et al., 2017). Hosseinvand and Sohrabvandi (2016) assessed the effect of adding pectin, inulin, and β-glucan for producing low-fat mustard sauce. Additionally, they mentioned that 25% of inulin and 25% of pectin could be considered as appropriate for replacing with fat because of obtaining maximum firmness and adhesiveness and minimum stickness. These differences can be related to their maximum water-holding capacity in formulation, fat existing in emulsion, and dietary fibres, which are fundamentally caused by increasing emulsion viscosity because of utilizing carbohydrate-based fat alternatives based on the formulation of low-fat foods. Worrasinchai et al. (2006) explained this behaviour because of increasing emulsion elasticity and mutual connection between polymeric chains for forming a three-dimensional lattice by adding hydrocolloids.

Only the square effect (p < 0.01) was obtained as significance for date syrup. Based on the results, synersis percentage increased parabolically by enhancing date syrup level from 0 to 4.5%. With the increase of date syrup and because it has many sugars and monosaccharides and on the other hand due to the low pH of ketchup sauce, the amount of organic acids such as acetic acid due to the decomposition of simple sugars compared to the control sample, increased significantly, and with increasing acidity, the possibility of pectin network formation increases and this leads to greater strength of pectin network than the control sample and increase its water absorption capacity (Nasir et al., 2014). Date syrup possesses the higher percentage of insoluble content such as insoluble fibres compared to sugar does, which can be regarded as a reason for more brix in sugar-containing samples. Additionally, the viscosity of product enhanced by improving date syrup concentration because of removing most of its impurities (Cepeda and Villaran 1999), which is directly related to the results of the present study until adding 2.25% of date syrup, while an inverse relationship is observed by increasing the value up to 4.5%. Date syrup contains high amounts of fiber as well as mucilage compounds, which as a result of the existing fiber increases water retention in ketchup sauce. As the amount of fiber in the product increases, the dry matter of ketchup sauce increases and as a result, the ability to retain moisture in the sauce increases.

Furthermore, emulsion structure became stronger and adhesiveness increased by improving synersis percentage and enhancing inulin value in emulsion since more inulin can form stronger gel and higher water uptake (Keenan et al. 2014). Considering the results related to the mutual effect of these variables, an increase in inulin level resulted in enhancing synersis first and then decreasing, while it reduced first and then increased by adding date syrup. Since pectin compounds in tomato products lost their natural and primary state, they cannot play an appropriate hydrocolloid and consistency role. In fact, cell walls are ruptured during extracting tomato juice. After blanching, a portion of the pectin methoxylase enzyme of tomato, which still remained active, is released, affects pectin chains, breaks the ester bonds of methyl, and produces pectic acid. Accordingly, it cannot play the hydrocolloid role of anatural pectin. Thus, an increase in the percentage of separating serum from tomato products is considered as natural and often decreased by utilizing fibres and hydrocolloids (Giannouli et al. 2004).

Synersis=+0.471-0.887A-0.850B+4.563AB-6.103A2+11.298B2 4

Assessing the effect of independent variables on the level of sensorial properties

The effect of inulin and date syrup on the level of sensorial properties such as flavour, colour, texture, and overall acceptance in ketchup is displayed in Fig. 2. The higher sensorial scores were mostly achieved in inulin-containing prebiotic samples, especially those having higher inulin. Based on the data analysis, inulin influenced sensorial properties positively and an enhancement of its value up to 7.5% represented an upward trend (p < 0.0001). Acquiring greater score regarding product texture and appearance by adding inulin confirmed the positive effect of this hydrocolloid on ketchup texture due to the formation of gel structure by inulin in continuous phase and appropriate reaction between inulin and other ingredients in the product, which results in trapping water and increasing viscosity in product. The similar results were already attained about an enhancement in the consistency of the product by adding inulin and its effect as a water-bonding compound and its consistency role (Bortnowska and Makiewicz 2006). In addition, adding date syrup into ketchup affected colour highly, confirmed by the significance of its linear (p < 0.0001) and square effects (p < 0.05). According, an improvement of date syrup value from 0 to 2.5% resulted in no significant change in ketchup colour, while its colour enhanced by continuing the increase up to 4.5%. The statistical assessment of the samples demonstrated the insignificant effect of raising date syrup level on the sensorial properties including the flavour, texture, and overall acceptance of ketchup because of leading to the changes in product colour and flavour and consequently deterrent property during consumption, especially for overall acceptance. Perceiving the sweetness of date syrup quickly is considered as one of its unique properties. Additionally, date syrup is rapidly felt unceasing, while sucrose sweetness is sensed later and longer (Ashraf and Hamidi-Esfahani 2011).

Fig. 2.

Fig. 2

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Response surface curves for sensorial properties and specifying the effectiveness of independent variables

The color of food products is regarded as one of their important properties and can even influence consumer perception about food ingredients by considering the effectiveness level of each component on product colour. Based on the results of ANOVA, inulin and date syrup could be effective on the color of samples. In general, emulsion colour is affected compared to that of aqueous phase, accordingly the presence of polysaccharide digestible materials such as gums prevents oil particles in emulsion from inter-correlating by increasing the concentration of continuous phase. Thus, their higher capability in water uptake results in producing smaller particles and creating brighter color, and inulin leads to more color brightness and improvement in product compared to other combination factors do because of containing gum (Bouyer et al. 2012). According to McClements and Demetriades (1998), emulsion color varied from bright white to grey by increasing particle size. The results of ANOVA related to the mutual effect of inulin and date syrup indicated that an enhancement in inulin value raised flavour first and then reduced, while improving date syrup value failed to change product flavour. In addition, a similar trend was observed regarding the effect of enhancing inulin level on color (optimum level = 5.63), while color linearly improved by increasing date syrup value (optimum level = 1.13). The mutual effect of these variables confirms an increase and decrease in texture quality by enhancing inulin and date syrup value, respectively. In fact, inulin can bond other ingredients in the product and improve textural quality in product due to its lattice and polysaccharide structure, while date syrup reduces the quality because of having fiber and other ingredients (Al-Farsi et al. 2006). The consequence of the effectiveness level related to all of the textural and non-textural properties of a product on consumer is considered as its overall acceptance. Additionally, the samples with more firmness and viscosity are more accepted compared to other samples do. Based on the results related to the mutual effect of inulin and date syrup on the overall acceptance of ketchup, adding more inulin and date syrup into product led to a primary increase in overall acceptance, while it decreased severely. In fact, an enhancement in the value of the factors results in changing product with respect to color and flavour, following by deterrent property during consumption.

Taste=+18.4+0.125A-0.625B-0.551AB-1.210A2-0.701B2 5
Color=+16.8+0.125A+0.375B-0.751AB+0.975A2+0.475B2 6
Texture=+18+0.375A-0.375B+0.502AB+1.251A2-1.250B2 7
Generalacceptance=+18.6+0.253A-0.375B+0AB-0.675A2-1.425B2 8

Assessing the effect of independent variables on the level of sensorial properties

Figure 3 represents the effect of the independent variables involving inulin and date syrup on the acid-resistant bacteria, as well as mould and yeast colonies of ketchup as three-dimensional response surface curves.

Fig. 3.

Fig. 3

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Response surface curves for microbial properties and specifying the effectiveness of independent variables

Considering the coefficients related to independent variables in the suggested model (Eq. 9), inulin failed to affect significantly acid-resistant bacteria in ketchup (p < 0.05) so that bacteria count increased linearly and slightly by enhancing its value. Inulin as a prebiotic material can produce organic acids such as lactic, acetic, and propionic acid, accordingly it can limit the growth of acidic environment-sensitive pathogens by acidifying the environment. While prebiotics are themselves resistant to acidic pH (Holo et al. 1991). As shown in the response surface curve in Fig. 3, only the linear (p < 0.0001) and square effects (p < 0.05) of date syrup on the changes in the acid-resistant bacteria of ketchup are significant among above-mentioned independent variables. In other words, an increase in its value in ketchup resulted in decreasing bacteria count significantly. Date syrup can reduce pH and create an acidic environment because of possessing multiple sugar sources such as glucose and fructose, as well as usable sources for bacteria such as organic acid-producing ones, which influences appropriately the decrease of harmful bacteria in produced sauce (Bensmira and Jiang 2011). Based on the results obtained from ANOVA for the mutual effect of these variables, a reduction was observed in bacterial filaments value by enhancing inulin and date syrup value. In the present study, a portion of decrease in bacteria count can be related to the pasteurization heating in ketchup. Further, ketchup is considered as an inappropriate environment for surviving bacteria due to its low pH, free water restriction because of using hydrocolloid compounds in the formulation, and thermal process application.

Bacteria=0+0A+0.416B+0AB-0.208A2+0.416B2 9

The coefficient of independent variables in Eq. (10) demonstrated the partial effect of inulin in increasing the level of mould colonies, confirmed by the significance of its square effects (p < 0.05). Thus, the existence of mould in ketchup did not change significantly by varying the percentage of inulin form 0 to 3.75%, while an upward trend was observed after enhancing the value up to 7.5%. These conditions are inconsistent with those of the studies conducted on inulin in the field of decreasing mould and yeast count since inulin as a prebiotic compound can be used as an effective material to prevent microbes from growing in foods. Inulin decomposition and short-chain acid production result in reducing pH and consequently preventing the growth of microbes. In general, the antimicrobial effect of plant polysaccharides can be caused by combining with membrane probiotics, decomposing cytoplasmic membrane, changing cellular ionic charge, coagulating interacellular materials, and preventing enzyme production in microbial cell (Gutierrez-Pacheco et al. 2016; Krivorotova et al. 2016). Considering the assessments, the linear (p < 0.0001) and square effects (p < 0.05) of date syrup were determined as significant in provided model among the independent variables affecting the changes in the level of mould colonies in ketchup. For example, Ismail and Altuwairki (2016) reported the strong deterrent effect of the methanolic extract of date pulp on alternaria, fusarium, penicillium, and aspergillus moulds and an increase in the diameter related to the zone of inhibition of mould by enhancing extract concentration. Further, penicillium and fusarium represented more sensitivity to methanolic extract compared to other moulds. In another study, Candida albicans treatment led to the weakness and partial collapse of cell wall, as well as deep effects of cell lysis, cytoplasmic material leakage, and even cell death at higher concentration. In general, the chemical compounds of plants affect multiply moulds and the use of date extract as a pharmaceutical material was considered as probable. Laboratory studies indicated flavonoids as the possible responsible for the anti-mould properties of date extract (Baliga et al. 2011). Based on the analysis of the results related to the mutual effect of inulin and date extract, a primary decreasing and secondary increasing trend was observed in the level of mould by enhancing inulin value (optimum value = 5.63), while it improved linearly by raising date syrup value (optimum value = 1.13).

Mould=+3.5-0.167A+0.167B-0.251AB+0.351A2+0.100B2 10

Evaluating the presence of yeast colonies in produced ketchup represented that yeast growth increased by adding more inulin, confirmed by the significance of its square effect (p < 0.05). Accordingly, the change in inulin percentage from 0 to 3.75% resulted in decreasing the amount of yeast colony in ketchup, while it increased when the percentage enhanced from 3.75 to 7.5%. The square effect of date syrup (p < 0.01) was only determined as its significant effect. The results demonstrated a linear increase in yeast presence by improving date syrup value from 0 to 4.5% (Fig. 3). Numerous studies reported the relationship between the antimicrobial activity of extracts and their phenolic content. In general, the higher concentration of extract or its phenolic compounds leads to their more antibacterial properties to food pathogen and other microorganisms. The mechanism related to the effect of these compounds includes disrupting cytoplasmic membrane, proton-motive force, and electric current and coagulating cellular content (Lambert et al. 2001), which are inconsistent with the results of the present study about using date syrup. In fact, the results of analyzing the effect of process variables on the presence and growth of yeast in sauce indicated the significance of the square effects of both variables including inulin and date syrup in the obtained model for yeast. Based on the results related to the mutual effects of two variables, an increase in inulin value resulted in enhancing the level of yeast linearly (optimum value = 1.88), and the amount of the yeast formed in the product improved by raising date syrup value (optimum value = 2.25).

Yeast=+3.10+0A-0.0803B-0.500AB+0.008A2+0.133B2 11

Optimizing ketchup formulation

The operating conditions of optimizing ketchup formulation by using the specific weight percentages of inulin and date syrup were probed through numerical optimization method in Design-Expert software on the physicochemical (pH, brix, and synersis percentage), sensorial (flavour, color, texture, and overall acceptance), and microbial parameters (acid-resistant bacteria, mould, and yeast count). To this end, the objectives of optimization were first specified and response surfaces and independent variables were then regulated. In addition, the minimum and maximum values of physicochemical, sensorial, and microbial properties were respectively considered as the minimum and maximum data obtained from analysing mentioned properties. Further, target values included the data related to the best sample with respect to overall acceptance, which were determined in sensorial analysis. The values of the independent variables including inulin and date syrup under the optimum conditions of ketchup formulation were obtained as 3.75 and 1.13% (w/w), respectively. Finally, a formula possessing all of intended physicochemical, sensorial, and microbial properties at optimum level simultaneously was determined. Table 2 summarizes the required level of two intended independent variables for producing optimum ketchup and response of each dependent variables achieved in optimum sample by using these three materials.

Table 2.

Ketchup sample formulation with optimized properties

Independent variable Minimum Maximum Optimal value Response Quantity
Inulin (%) 0 7.5 3.75 pH 3.55
Brix 25.20
Date syrup (%) 0 4.5 1.13 Synersis (%) 14
Sensory characteristics 17.25
Bacteria 0
Mould 3.5
Yeast 3.1
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Conclusion

Nutrition fact, colour, flavour, and consistency are considered as the most important qualitative aspects of tomato-processed products, which affect consumer buying behaviour significantly. The present study evaluated the performance of the inulin as a well-known prebiotic, as well as date syrup as by sucrose alternative, by representing the significant role of inulin and date syrup in improving the texture of synersis and brix, sensorial properties and overall acceptance of the product, respectively. Regarding the assessment of microbial parameters, an increase in inulin value from 3.75 to 7.5% resulted in growing acid-resistant bacteria, mould, and yeast in ketchup, while a reverse trend was observed by enhancing date syrup value, by indicating its appropriate effectiveness against microbial corruption.

Footnotes

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Contributor Information

Davood Mirzaei, Email: d_mirzaie72@yahoo.com.

Ahmad Pedram Nia, Email: ahmadpedram@yahoo.com.

Mahdi Jalali, Email: mehdijalali62@yahoo.com.

References

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