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. 2022 Feb 21;60(5):1493–1504. doi: 10.1007/s13197-022-05398-0

A review on some properties of almond: ımpact of processing, fatty acids, polyphenols, nutrients, bioactive properties, and health aspects

Mehmet Musa Özcan 1,✉
PMCID: PMC10076465  PMID: 37033309

Abstract

This review was focused on the proximate compounds, nutritional values, total phenolic, flavonoid, antioxidant activity, fatty acid profile, polyphenols, health aspects and uses of almond kernel and oils. Almond contained about 24–73% crude oil, 50–84% oleic and 6–37% linoleic acids, 77–3908 mg/kg β-stosterol and 5–8 mg/100 g β-tocopherol. Almonds are a good source of mono- and unsaturated fatty acids, phytochemicals, bioactive components, minerals, vitamin E, polyphenols and phytosterols and at the same time almonds have healing effects. Since almond seeds or seed oils have versatile uses, they are consumed on their own or as part of a range of food products. Almonds are considered a healthy snack when consumed due to their potential cardioprotective effects. Since the composition of almonds and its effects on health will be effective both during cultivation and processing, studies should be carried out in a way that preserves the product quality.

Graphical abstract

In this study, the proximate compounds, harvest and irrigation effect, nutritional values (protein, amino acids, vitamins minerals), total phenol, flavonoid, antioxidant activity, fatty acid profile, polyphenols, and uses of almond kernel and oils were summarized.

graphic file with name 13197_2022_5398_Figa_HTML.jpg

Keywords: Almond, Nutrients, Phytochemicals, Bioactive properties, Polyphenols, Traditional using

Introduction

Almond (Prunus amygdalis var. dulcis), an important perennial plant belonging to the Rosaceae family, is one of the oldest grown nut tree crop in the world, and it is an important nut tree cultivated in the hot-arid countries of the Mediterranean basin (Piscopo et al. 2010; Summo et al. 2018). The almond group consists of two types, Prunus dulcis (sweet almond) and Prunus amara (bitter almond), and sweet almonds contain approximately 50% oil on average. The demand for almond cultivation is increasing day by day due to its easy adaptation to arid climate and unfavorable soil conditions. The annual production amount of almond, which is among the most valuable edible nuts, is approximately 1.7 million metric tons, and it is among the most grown species in Mediterranean countries (approximately 28% of world production occurs in this region (Yıldırım et al. 2016; Hosseinzadeh et al. 2019). The weight of almonds ranges from 2.66 g (Bonita) to 13.22 g (Amendoao) (Oliveira et al. 2018). Almond, a valuable industrial raw material, is grown in many parts of the world and consumed as dried nuts (Piscopo et al. 2010; Colic et al. 2017). Almond is very favorable in terms of almond cultivation and diversity in different regions of Turkey (Özcan et al. 2011; Kırbaşlar et al. 2012). Almond oil, which has been used for many years for cosmetic and medicinal purposes, also shows similarities with the fatty acids of other Prunus seed oils such as apricot or plum (Özcan et al. 2011; Colic et al. 2017; Al-Juhaimi et al. 2018). In addition, almonds are edible in their natural form and are used as a main ingredient in many local foods and have an economical value. Almonds are grown for their fruit in much of the world (Tiwari et al. 2010). Almonds, considered a valuable source of protein in the human diet, are mostly consumed in shell. In addition, almonds are blanched and peeled, then ground and used to flavor milk drinks or confectionery. Almonds are also used fresh (Bolling 2017). It is necessary to well characterize the bioactive properties of almonds to better characterize the potential health benefits of almond kernels (Nanos et al. 2002; Piscopo et al. 2010). In most of the almond oil samples, oleic, linoleic, palmitic and stearic acids accounted for more than 99% of the total fatty acid content (Colic et al. 2017). The oil amount and fatty acid composition of almond and kernel oils vary depending on the genotype, variety, climate, maturity stage, harvest time and environmental conditions. In addition to the fatty acid profile, almonds have also been noted to be rich in protein, fiber, minerals, tocopherols, phytosterols, and other bioactive compounds (Matthäus and Özcan 2020; Banjanin et al. 2021). Almonds, an important fat crop in many parts of the world, are also an essential dietary ingredient acting as sources of energy and functional compounds. This review summarizes the proximate compounds, harvest and irrigation effect, nutritional values (protein, amino acids, vitamins minerals), total phenol, flavonoid, antioxidant activity, fatty acid profile, polyphenols, and uses of almond kernel and oils.

Effect of harvest, irrigation on chemical composition

The chemical compositions of almonds (sugar contents, fatty acid profile and polyphenols) are significantly affected by harvest time, variety, environmental factors, several physiological factors, agriculture practices, ripening and genotype. The nutritional value of unripe almond, a valuable niche product, has attracted considerable attention (Piscopo et al. 2010; Yada et al. 2013; Summo et al. 2018). There was an increase in oleic acid during maturation (Piscopo et al. 2010). In addition, it has been reported that phenolic contents change over the years. It has been reported that fungi, bacteria, pests, air and light, environmental factors in the area where it is grown, cultivation techniques, fruit ripeness, location, genetic characteristics of the varieties, soil characteristics are effective in the formation of this difference (Esfahlan and Jamel 2012). Nanos et al. (2002) investigated the effects of harvest time and irrigation strategies on lipid content, lipid quality and sugar content of two almond varieties (Texas and "Ferragnes"). Almond, produced worldwide, usually fresh or consumed as a component of various dishes after technological processes, is a major food (Larrauri et al. 2016) and is an important food product in addition to local use as a dried nut. It is very important to keep nuts in good quality in order to protect the physical properties and chemical composition of the nut in the nut harvest (Banjanin et al. 2021). It has been reported that early harvested almonds have better nutritional quality, since late harvested almonds have lower unsaturated/saturated fatty acids than early harvested almonds. In addition, late harvested almonds have been reported to have higher sucrose and lower inositol and large amounts of sugar than early harvested almonds. The quality properties of the almonds was significantly influenced by harvest time and at harvest time caused an increase in the lipid content of the almonds as well as a decrease in their carbohydrate and protein contents. In addition, ash content remained constant during maturation (Summo et al. 2018). Traditionally, immature almonds are consumed fresh in a very short period depending on seasoning when they can be found naturally during the production phase. However, immature almonds can be stored frozen and then consumed all year round. At the same time, immature almonds meet the expectations of consumers who are aware of the relationship between healthy nutrition and well-being (Summo et al. 2018). Variety and location factors such as harvest year and irrigation management (Zhu et al. 2015a) also affected the α-tocopherol contents in almonds. In another study, while the oil content of “Ferragnes” and “Texas” varieties grown in two different regional trial fields in Greece were not affected by irrigation, some differences in the fatty acids were detected (Nanos et al. 2002).

Processing and storage

One of the most common heat treatment methods applied to nuts in the world is roasting, which is a heat treatment involving dehydration (Lin et al. 2016). Depending on the color and moisture content, almonds roasted in different ways can be light, medium or dark in color. Roasting should be done in well-defined conditions to protect almond oils from the oxidation of unsaturated fatty acids and to prevent off-flavor formation and preserve their nutritional properties (Grundy et al. 2015a, b).

It has been stated that hot air roasting causes little weight change in all almond kernels due to water evaporation of water in kernels. However, as the endoplasmic network of fat masses in almonds is destroyed by roasting, the process of roasting greatly affects the volume of the extracellular pores where the oils are located, the structure of the almond cell walls and also the intracellular fat masses (Grundy et al. 2015a). It has been reported that oils become more fluid due to the breakdown of fat cells in oil seeds, coagulation of the protein, adjustment of the moisture content to the optimum value for extraction and a decrease in oil viscosity with heat treatment. It has been stated that the preference of roasted almonds may increase in terms of flavor due to the release of oils during the roasting process. Heat treatment has an effect on the fatty acids of seed oils (Akinosa et al. 2011). Light and pale amber almond oil (Özcan et al. 2020), which is usually extracted from almond kernels by cold pressing, is extracted by solvent or supercritical liquid extractions. Raw and roasted almonds contain phytochemicals as well as for other foods. It has been stated to be a useful food and ingredient (Nishi and Kendall 2014).

It has been reported that almonds consumed in raw form (roasted or unbleached) should be pasteurized against bacterial, mold and fungal contamination or to remove any contaminants. A water activity of less than 0.65 is required to inhibit microorganism growth in stored almonds. Low temperature and low humidity storage conditions are among the basic parameters that should be applied during a process that will affect the moisture contents of almonds and increase lipid oxidation (Lin et al. 2016). In addition, the quality of almond kernels is affected by loss of texture, color and/or taste and by uncontrolled storage environments such as stale, rancidity, the development of disease and / or insect damage. The quality of stone fruits will decrease significantly after a long storage period and transportation after being exposed to an intense fatty acid oxidation, the oleic/linoleic acid ratio is characterized as the criteria that determine the quality of the kernel. Changes in soluble sugar content in almonds in three consecutive harvest years have been reported to affect the sugar amount in nuts, such as variety, seed maturity, growing conditions and growth position (Yada et al. 2013).

Consumption and using

Almond kernel, which has a widespread use all over the world with its applications in the food sectors, is used as an ingredient in other processed foods such as snacks. Since almond seeds or seeds have versatile uses, they are consumed on their own or as part of a range of food products. Almonds grown worldwide and having the highest economic value among nuts are the most produced in the United States and consumption of almonds is high worldwide. Almonds, which are mostly consumed raw, sliced or roasted, are also widely consumed as almond butter. In addition, it is also available as almond milk and oil (Bernat et al. 2015). In addition to the fact that almond is generally consumed as a snack, it is also added to the composition of various sweet and savory dishes and food products. Due to the high oil content of almonds in the confectionery industry, it reduces the water absorption of marzipan (Izaddost et al. 2013). However, in most countries of the world, roasted almond kernels are considered by consumers as a popular snack item (Lin et al. 2016). Dried fruits, confectionery and marzipan production; Almond oil, which is used in many areas such as the ice cream industry, cream cake and chocolate industry, is used in the pharmaceutical, paint and cosmetics industry. It is also important in terms of the use of the green shell of almond as animal feed and the use of its hard shell in the production of fuel and chipboard (Yıldırım et al. 2016).

Fatty acid profiles of almonds oils

The some fatty acid, tocopherol and sterol contents of previous studies are given in Table 1. In previous studies, the ratio of oleic acid to linoleic acid can be used as a criterion in determining the quality of almond kernel. As a result of roasting almond kernels, the levels of unsaturated fatty acids of oils were observed to increase depending on the applied temperature (150 and 180 °C) and the time (5, 10 or 20 min) (Lin et al. 2016). The consumption of almonds is increasing due to its high nutritional content as a nutritional stabilizer and its high monounsaturated and polyunsaturated fatty acid contents (Özcan et al. 2011). In fact, most studies have reported a predominance of major fatty acids (oleic, linoleic, palmitic, and stearic) in almond oils (Zhu et al. 2015a; Colic et al. 2017; Zamany et al. 2017; Rabadan et al. 2017). The α-linolenic contents of almond oils varies depending on various factors (Zhu et al. 2015a; Chodar-Moghadas and Rezaei, 2017). The positive effect of almond consumption on health is mostly related to the monounsaturated fatty acids (Tey et al. 2015).

Table 1.

The some fatty acid, tocopherol and sterol contents of previous studies on almond kernel oils

Fatty acids (%) Tocopherol mg/100 g mg/kg Sterols mg/kg mg/100 g μg/g
Myristic 0.01–1.27 α-tocopherol 1.60–84.0 136.33–945.41 Cholesterol 0.13–9.8
Palmitic 2.21–15.13 α-tocotrienol 0.174–0.236 – Brassicasterol 3.8–11.2
Palmitoleic 0.03–2.50 β-Tocopherol 5–8 0.73–10.53 24-methylencholesterol 0.03–8.6
Stearic 0.07–3.97 ¥-tocopherol 0.14–0.84 6.42–77.87 Campesterol 2.46–172.3 4.9
Oleic 50.40–84.0 δ -tocopherol 0.01–1.264 0.10–2.86 Campestanol 0.09–4.3 3.3 134
Linoleic 6.21–37.10 Stigmasterol 0.86–99.1 5 55
¥-linolenic 0.06 δ-7-Campesterol 0.78–16.3
α-linolenic 0.02–11.10 δ-5,23-stigmastadienol 1.3–17.2
Arachidic 0.03–0.20 Chlerosterol 26.1–56.0
Behenic 0.006–0.95 β-stosterol 77.28–3908 143.4 580
Arachidonic 0.04–0.38 Sitostanol 1.91–94.8 3.2
δ-5-avenasterol 9.89–581.7 19.7 32
δ-5,24-stigmastadienol 1.48–47.5
δ-7-stigmasterol 1.94–73.3
δ-7-avenasterol 1.39–30.8
(Kazantzis et al. 2003; Özcan et al. 2011; Kırbaşlar et al. 2012; Yıldırım et al. 2016; Lin et al. 2016; Grundy et al. 2016; Colic et al. 2017; Fernandez et al. 2017;Summo et al. 2018; Oliveira et al. 2019; Özcan et al. 2021) (Senesi et al. 1996; Martins et al. 2000; Kornsteiner et al. 2006; Yada et al. 2013; Yıldırım et al. 2016; Grundy et al. 2016; Fernandes et al. 2017; Matthaus et al. 2018) (Dulf et al., 2010; Yıldırım et al. 2016; Fernandes et al. 2017; Matthaus et al. 2018; Matthaus and Özcan, 2020)
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Tocopherols

The α-, β-, ¥ - and δ-tocopherols have been described to differ according to the number and location of methyl substituents in the chroman ring (Azzi et al. 2000; Saldeen and Saldeen 2005). It has been reported that α-Tocopherol content is ten times higher than δ- and ¥ -tocopherol amounts and this feature can be used in almond breeding studies. In addition, it has been reported that α-tocopherol is predominant in nuts, mainly almonds. In general, the fruit with the highest tocopherol content among nuts is almond (Izaddost et al. 2013). The main tocopherols that are present in sufficient amounts in almond kernel and are effective in maintaining quality are α-, β-, δ- and ¥ -tocopherols. Almond seed oils contain 187 to 490 g/kg α-tocopherol, followed by and isomers thereafter (Kırbaşlar et al. 2012). In addition, α-tocopherol has been reported to be the predominant tocopherol in almonds, hazelnuts and macadams, and with regard to its antioxidant potential, nuts have been reported to be an excellent source of tocopherol and polyphenols. Since tocopherols (α-, β-, ¥ - and δ-Tocopherols) and tocotrienols (α-, β-, ¥ - and δ-tocotrienols) are compounds with different vitamin E activity produced only in plants, α-Tocopherol is the most biologically active E vitamin form. These vitamin E isoforms have been reported to have antioxidant properties and protective roles in biological systems (Sen et al. 2007).

Polyphenols of almonds

The some phenolic compoundss of previous studies are given in Table 2. Phenolic compounds form a large and heterogeneous group of secondary plant metabolites widely distributed in the plant kingdom. Generally, tocopherols and polyphenolic compounds constitute important biological properties of nuts. Groups called phenolic acids, flavonoids, proanthocyanidins, and tannins are the key phenolic compounds of nuts (Bodoira and Maestri 2020). However, the probable reason for the differences in the polyphenol content of almonds in the literature depends largely on the type of extraction solvent and the standards used, variety, genotype, climatic factor and agricultural conditions (Salcedo et al. 2010). Eight of almonds commonly grown in California did not contain p-hydroxybenzoic acid and kaempferol, gallic acid and quercetin were identified in almond genotypes selected. The most abundant polyphenol in almond was catechin, and followed by chlorogenic acid and naringenin in descending order (Colic et al. 2017). It has been reported that the dominant pheolic component of Turkish and Serbian local and commercial almonds is catechin (Yıldırım et al. 2016; Colic et al. 2017; Banjanin et al. 2021). In another study, gallic acid, 3,4-dihydroxybenzoic, ( +)-catechin, 1,2-dihydroxybenzene, syringic acid, caffeic acid, and quercetin are the main phenolic components of almond kernels. The phenolic content varies according to the almond type and the catechin amounts of almond kernels were found between 0.5 and 3 mg/kg, the epicatechin amount is 0.3 mg/kg and 0.7 mg/kg, the kaempferol amount is 0.2 mg/kg and 1.4. It has been reported that the content of mg/kg, and naringenin ranges from 0.2 to 0.8 mg/kg. In addition, almond kernel shell is richer in polyphenol than kernel, and almond seed husk contain izorhamnetin rutinoside, izorhamnetin glucoside, piceid (a derivative of resveratrol), glucosides, rutinosides, kaempferol rutinoside, protocathecuic acid, 3'-0-methyl quercetin, acidlorogenic acid, trans-p-coumaric acid, flavonoids, kaempferol, isorhamnetin and kaempferol glucoside (Mandalari et al. 2010a; Xie and Bolling 2014).

Table 2.

The some phenolic compoundss of previous studies on almond kernels

Phenolics mg/kg Phenolics µg/100 g Phenolics mg/g Vitamins mg/100 g
Protocatechuic a 0.32–1.20 (−)-epicatechin 11.38–99.35 Gallic acid 0.04 Riboflavin 1.0–1.1
p-hydroxybenzoic a 0.19–0.69 (−)-gallocatechi gallata 3.24–104.08 Protocatechuic a 0.88 Vitamin E (α-tocopherol) 25–27
Ellagic a 0.02–0.35 ( +)-catechin 569.09–1109.9 5-Hydroxybenzoic a 1.26 Biotin 0.01–0.90
Vanillic a 0.38–2.84 Chlorogenic acid 72.78–318.14 Vanillic a 0.94 Folate 0.10–0.13
Chlorogenic a 0.47–21.03 Cis-p-coumaric a 5.83–71.88 Chlorogenic a 1.61 Niacin (B3) 1.5–3.7
Caffeic a 0.43–2.80 Eriodictyol 22.52–150.74 t-p-Coumaric a 0.09 Pantothenic acid 0.36–0.38
p-coumaric a 0.03–0.72 Gallic acid 48.01–440.54 Catechin 0.20 Pyridoxine (B6) 0.08–0.16
Ferulic a 0.11–2.81 Hydroxybenzoic acid 65.47–162.07 Naringenin 0.28 Riboflavin (B2) 1.0–1.1
Sinapic a 0.56–3.50 Isorhamnetin 5.39–182.88 Kaempferol 0.02 Thiamin (B1) 0.19–0.25
Resveratrol 0.06–0.12 Isorhamnetin-3-o-glucoside 12.66–295.54 Isorhamnetin 0.04
Catechin 2.67–117.59 Naringenin 12.02–137.86 Epicatechin 0.16
Rutin 0.61–11.33 Protocetchuic acid 40.57–105.02 Eriodictyol 0.01
Naringin 0.04–0.11 Quercetin-3-o-rutinoside 1.96–2.40 Quercetin 0.01
Luteolin 0.34–4.27 Trans-p-coumaric a 67.53–196.94 (Lin et al. 2016)
Apigenin 0.10–10.47 Vanillic acid 30.59–131.08
Naringenin 0.05–14.49
Kaempferol 0.04–2.63
Isorhamnetin
Quercetin
Gallic acid 0.67–3.26
Epicatechin 0.53–27.57
Colic et al. 2017; Oliveira et al. 2019; Banjanin et al. 2021 (Richardson et al. 2009; Yada et al. 2013; Grundy et al. 2016)
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Protein, mineral, dietary fiber, and vitamins contents of almond kernels

The physico chemical properties of previous studies on almond kernels are given in Table 3.

Table 3.

The physico chemical properties of previous studies on almond kernels

Proximate compositions % Minerals mg/100 g ppm mg/g Amino acids µg/g protein / %
Moisture 3.60–7.27 Ca 185–678 1.83–2.94 Histidine 8–12 / 1.11–1.50
Ash 1.67–8.13 Mg 30–513.4 2.98–4.04 Isoleucine 26–27 / 1.34–1.94
Oil 24.88–73.94 P 253–800.0 7.93–9.38 Leucine 54–56 / 2.80–3.45
Protein 13.48–24.51 K 7.66–2051.1 13.14–15.10 Lysine 5–6 / 1.36–1.58
Carbohydrate 11.00–27.6 Zn 5.1–80.50 3.0–88.44 0.04–0.06 Methionine + cystine 3–5 / 0.23–0.35
Energy value (kcal/100 g) 452–639 Cu 1.2–25.80 0.9–23.0 0.01–0.01 Phenylalanine + tyrosine 46–48 /1.14–1.47
Total sugar 1.2–6.00 Mn 2.2–37.83 1.2–33.95 – Threonine 27–30 / 1.34–1.62
Total dietary fiber 11–14 Fe 54.83–65.33 39.77–146.35 0.20–0.27 Valin 39–44 / 1.73–2.48
Sucrose (%) 70.6–85.3 Na 56.66–103.88 0.29–0.38 Aspartica 79–85 / 4.25–5.70
Inositol (%) 2.36–7.96 Glutamica 264–276 7 8.46–13.21
Raffinose (%) 1.23–4.84 Alanin 51–55 / 1.81–2.43
Physical properties Arginine 77–79 / 3.82–5.31
Kernel weight (g) 0.95–3.14 Glycine 62–63 /2.40–3.30
Thicknes (mm) 8.52–11.09 Proline 39–42 / 1.52–2.10
Lenght (mm) 20.33–35.77 Serine 39–42 / 1.69–2.41
Width (mm) 13.31–16.26
Width/lenght ratio 0.47–0.80
Barbera et al. 1994; Schirra et al. 1994; Kazantzis et al. 2003; Kornsteiner et al. 2006; Richardson et al. 2009; Özcan et al. 2011; Yada et al. 2013; Izaddost et al. 2013; Grundy et al. 2016; Yıldırım et al. 2016; Colic et al.2017; Hosseinzadeh et al. 2019; Summo et al. 2018; Oliveira et al. 2019) (Barbera et al. 1994; Schirra et al. 1994; Richardson et al. 2009; Özcan et al. 2011; Yada et al. 2013; Grundy et al. 2016; Hosseinzadeh et al. 2019) (Hosseinzadeh et al. 2019; Houmy et al. 2020)
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Protein

In general, protein contents for most almonds range from 16 to 23 g/100 g and methionine, lysine and threonine amino acids come in abundance (Ahrens et al. 2005). The so-called almond major protein, amandin is the main storage protein found in almonds and belongs to the class of legume seed proteins (Kshirsagar et al. 2011). It has been reported that the amount of globulin and albumin in almonds constitutes 88–91% of the total protein. The amounts of essential amino acids that make up about 30% of the protein in almonds have been reported to be some differences between their amino acid contents, even if they are grown in the same region. In addition, methionine, lysine, and threonine have been reported to be the first, second, and third limiting amino acids in amandine which the main storage protein in almonds.

Minerals

Minerals in plant tissues, including seeds such as almonds, are affected by the mineral content of plant tissues, many environmental factors, agronomic practices, geographical location of plants or trees, soil composition, water source, irrigation, and fertilizer components (Özcan et al. 2011, 2020; Colic et al. 2017; Banjanin et al. 2021). The most abundant mineral elements typically found in plants are potassium, calcium, magnesium, iron, zinc, magnesium, manganese, phosphorus, sulfur and nitrogen (Özcan et al. 2011).

Dietary fiber

Crude fiber and pentosans were found in almond varieties. The totality of these ingredients has been defined as "dietary fiber". The hemicellulose, cellulose and lignin contents of almond kernels differed during the development. Studies have been carried out on polysaccharides that form the cell wall material of almond kernels and shells. In addition, monosaccharides such as arabinose, uronic acids, glucose, xylose, galactose, rhamnose, fructose and mannose have been reported to be found in seeds and shells in varying proportions (Mandalari et al. 2010b). Almond kernels contain about 5.5% carbohydrates and 11.8% dietary fiber (ie cell walls). The walls of almonds have been shown to be rich in arabinose, uronic acid, glucose, xylose and galactose (Ellis et al. 2004).

Proximate and bioactive compounds

The bioactive compound and antioxidant activity values of previous works on almond kernels are shown in Table 4. Recently, works have focused on revealing the potential bioactive and beneficial compounds for human health in nuts (Lin et al. 2016; Summo et al. 2018). Lin et al. (2016) reported that almond extract produced 7.5 mg GAE/g (dw) total phenol, 2.43 mg catechin equivalent (CE)/g (dw) total flavonoid and 0.34 mg CE/g (dw) concentrated tannin. It has been reported that extracts of almond kernel, brown peel and green peel have a strong antioxidant activity. A study was conducted on the total oil content and concentration, total phenolic amount and antioxidant activity, the fatty acid profiles in the almond kernel oil samples (Colic et al. 2017). Almonds are also reported for their high antioxidant activity (Lin et al. 2016; Banjanin et al. 2021). Since the chemical compositions that determine the quality of almonds are taken into consideration, the oil amount and composition of the almond seed are of great importance (Colic et al. 2017; AlJuhaimi et al. 2018; Banjanin et al. 2021). Almond kernels have been reported to be a good source of vitamin (tocopherols, riboflavin) and minerals (Banjanin et al. 2021). It also contains proanthocyanidins, flavonoids and phenolic acids, and a wide variety of phenolic compounds responsible for their antioxidant properties which predominantly found in the skin (Mandalari et al. 2010b). Due to tocopherols (Kornsteiner et al. 2006), minerals (Özcan et al. 2011), phytosterols (Matthaus and Özcan, 2020), tannins and other phytochemicals with potential bioactivity, these properties make almonds nourishing and healthy. It makes a snack and can be used as a gradient in food formulation (Colic et al. 2017; Bodoira and Maestri 2020).

Table 4.

The bioactive compound and antioxidant activity values of previous Works on almond kernels

Bioactive properties Oil properties
Total carotenoid (µg/g) 0.21–1.85 Iodine value gI2/100 g 88.8–96.1
Total phenol (mgGAE/g) 0.27–7.5 Saponification number (mg KOH/g oil) 173.5–192.9
Total flavonoids (mgCE/g) 2.43–19.49 Refractive ındex 1.462–1.467
Vitamin E ( (mg/100 g) 9.99–19.42 Acid value (mgKOH/g oil) 0.26–0.30
ABTS (µg Trolox/g) 1.29–7.87 Peroxide value (meqO2/kg) 0.34–14.622
DPPH (µg Trolox/g) 1.2–30.72 Total wax (g/100 g) 2.05–2.53
FRAP (µg Trolox/g) 0.04–0.96 Acidity (%) 1.389–2.397
Condensed tannins (mgCE/g) 0.34 Unsaponifiable matter (g/100 g) 0.35–0.53
Total ellagic acid (mg/100 g (fw)) 627–872 (Kornsteiner et al. 2006; Özcan et al. 2011)
Squalene (mg/kg) 96.43–113.11
Richardson et al. 2009; Abe et al. 2010; Bolling 2017; Yada et al. 2013; Lin et al. 2016; Colic et al. 2017; Oliveira et al. 2019; Özcan et al. 2021)
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Traditional uses of almond

For both food and medicinal use, sweet almonds have been grown and consumed from west to east for thousands of years. Almonds have great potential in inhibiting the copper-induced oxidation of human LDL cholesterol and DNA cleavage induced by the hydroxyl and peroxyl radical, due to their flavonoid and phenolic components (Wijeratne et al. 2006). Ingestion of almonds positively affects cardiovascular and coronary heart diseases (Connell et al. 2000; Kendall et al.2002; Maguire et al. 2004; Kodad et al. 2006; Dourado et al. 2004; Forcada Fonti Kodad et al. 2011; Gupta et al. 2012;Matthäus et al. 2018). Also, when almonds were used in the diets of hyperlipidemic subjects, it significantly reduced coronary heart disease factors (Kendall et al. 2002). It has been reported that high-density lipoprotein cholesterol levels increase and plasma triacylglycerols and low-density lipoprotein cholesterol are significantly reduced in people consuming almond and almond oils. Edible kernels of plants belonging to the genus Prunus have been reported in folk medicine as soothing, anti-inflammatory, anti-hyperlipidemic, anti-tumor and antioxidants (Pellegrini et al. 2006). As a result of many metabolic studies in humans, it has been observed that consumption of almonds and other nuts reduces the risk factor of non-communicable diseases, especially type 2 diabetes, obesity, cancer, cholesterol and cardiovascular diseases (Tan and Mattes 2013; Nishi et al. 2014; Berryman et al. 2015). In particular, almonds are rich in proanthocyanidins, which contribute strongly to the stability of the gut microbiota and improve the immune response (Bolling 2017; Fan et al. 2017). Although saturated fatty acid increases the oxidative stability of almonds, it has been noted to be harmful to the cardiovascular system (Nishi et al. 2014; Berryman et al. 2015).

β-sistosterol is the most dominant phytosterol in almond kernels (Matthaus and Özcan, 2020). Since phytosterols reduce the LDL cholesterol concentrations in the blood, it has been stated that consuming almonds containing the phytosterols may contribute to the reduction of cardiovascular disease risk (Berryman et al. 2015).

Bitter almond

The fruit of Prunus amygdalus var. amara, almonds contain relatively large amounts of toxic phytochemicals called the glycoside amygdalin. The toxic tolerable doses of bitter almond for humans can lead to poisoning and death (Sanchez-Perez et al. 2012). Although bitter almond has various health benefits, it has been reported to have negative and toxic effects on the body as it contains hydrocyanic acid that gives almond bitterness (Toomey et al. 2012). The bitter almond variety has a predominantly bitter taste and this may be due to the presence of a diglycoside compound (amygdalin) in the kernels. Some studies have linked the bitterness of almonds to amygdalin. It has been reported that the benzaldehyde formed as a result of the hydrolysis of amygdaline is responsible for the bitterness in almonds. The concentrations of cyanogenic compounds such as amygdalin in plant seeds vary depending on the genotype and maturation levels of the seeds (Sanchez-Perez et al. 2012; Toomey et al. 2012). Amygdalin level can be affected by ecological factors, nitrogen concentration and its presence in the soil, and sudden temperature changes. Naringenin, kaempferol, caffeic acid, ferulic acid, hydroxycinnamic acid have been identified in the extract of bitter almond kernels (Moradi et al. 2017). Prunacin and amygdalin are the main constituents of bitter almonds, and prunacin is a cyanogenic monoglucoside detected in many almond organs. Different concentrations of prunacin are required in fruits for the synthesis of amygdala (Sanchez-Perez et al. 2012). When an almond containing amygdalin is chopped, glucose, benzaldehyde (bitter taste) and hydrogen cyanide (which is toxic) are released (Arrazola et al. 2012).

Healing effect of bitter almond

Bitter almond ointment or essential oil has been reported to be used in the treatment of acne, hemorrhoids, joint pain, hair loss. Amygdalin, which is more in bitter almonds, has been used to treat cancer for over 100 years (Zdrojewicz et al. 2015). It has been shown that amygdaline is an anticancer agent that can induce apoptosis and prevent adherence of cells. However, it has been noted that increasing doses may be more likely to cause cyanide-induced poisoning (Zdrojewicz et al. 2015).

Antimicrobial properties of bitter almond

It has been reported that bitter almond extract is effective in reducing Bacillus cereus colonies and monitoring the active toxin of this bacterium in foods. When it is combined with other herbs such as bitter almond and green tea, this effect is increased by creating synergy (Rasooly et al. 2015).

Conclusion

Almond is an important ingredient in food products as well as being consumed directly. Almond kernels are consumed as blanched, raw and roasted. Almonds are rich in phytochemicals, minerals, protein, amino acids, bioactive components and antioxidant properties that have beneficial effects on human health. It has been shown that amygdaline, a glycoside in bitter almonds, is an anticancer agent that can induce apoptosis and prevent adherence of cells. It is thought that factors such as variety, location, harvest time, agricultural conditions, processing, roasting, storage and climatic conditions are effective on the nutritional composition of almonds, which contain significant amounts of oil, protein, minerals, vitamins, fiber and phycochemicals.

Acknowledgements

Thanks to Dr Isam A Mohamed Ahmed and Mehmet Budak for their assistance in preparing the graphical abstract and shooting the original pictures.

Author contribution

This is not the case as there is only one author.

Funding

No funding.

Data and material availability

The data have been reviewed depending on the literature.

Code availability

There is no special software and code application.

Declarations

Conflict of interest

The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Consent for publication

This is not the case.

Consent to participate

Single author.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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