12
Nuts as Sources of Nutrients

João C. M. Barreira1,2, M. Beatriz P. P. Oliveira2, and Isabel C. F. R. Ferreira1

1 Mountain Research Centre (CIMO), School of Agriculture, Polytechnic Institute of Bragança, Portugal

2 REQUIMTE/LAQV, Faculty of Pharmacy, University of Porto, Portugal

As an introductory note, it should be highlighted that the chemical composition of nuts depends greatly on genotypic and environmental factors, such as growing region, cultivation methods, climatic conditions, harvesting years, and kernel ripeness (Muhammad et al. 2015; Yada et al. 2011). Therefore, some of the indicated values for typical parameters are characterized by having a wide variation range, due to the great variability of results among research groups.

12.1 Prunus dulcis (Miller) D. A. Webb (almond)

12.1.1 Botanical Aspects and Geographical Distribution

Almond, which belongs to the genus Prunus and the subgenus Amygdalus (Rosaceae), is a nutritionally important crop grown in many temperate and subtropical regions in the world. The cultivated almond is designated as Prunus dulcis (Miller) D. A. Webb, despite being also known as Prunus amygdalus Batsch and Prunus communis L., or less commonly as Amygdalus communis L. (USDA 2010).

Almond is one of the oldest cultivated nut trees in the world and a major nut tree crop in hot arid countries of the Mediterranean basin, although it spreads around the area included between the 36th and 45th parallels (Nanos et al. 2002).

12.1.2 Main Applications and Nutritional Overview

Almond seeds are classified as nuts, and are widely used, especially for direct consumption after toasting and for the confectionery industry and the production of sweets, cakes, and sugar‐coated almonds (Nanos et al. 2002). Almonds are eaten raw, roasted, and fried but they can also be used as ingredients in products such as sauces and snacks and marzipan and almond crunch. More recently, almonds are also being processed to make nutritional products such as almond milk used as a substitute for cow’s milk (Aranceta et al. 2006). In each case, the chemical composition is of great importance to establish nutritive value and quality to satisfy the concerns of consumers wanting a healthy lifestyle. The quality of nuts is defined in particular by moisture level, lipid content, oil composition, and oil ultraviolet absorption coefficients (Nanos et al. 2002).

Almonds are one of the most popular nut crops, being significant for human nutrition and health. These nuts are a nutrient‐rich source of lipids, protein, dietary fiber, minerals, vitamins, and polyphenols. The high nutritive value of almond kernels arises mainly from their high lipid content, which constitutes an important caloric source, without contributing to cholesterol formation in humans. Almond oil has been reported to be very rich in monounsaturated fatty acids, especially oleic acid, whereas saturated fatty acids are very low (Kodad et al. 2014).

Considering studies performed in Portuguese (Barreira et al. 2012a), American (Ahrens et al. 2005; Chen et al. 2006; López‐Ortiz et al. 2008; Martín‐Carratalá et al. 1998; Venkatachalam & Sathe 2006), Irish (Maguire et al. 2004), Spanish (Ahrens et al. 2005; Cherif et al. 2009; Piscopo et al. 2010), Italian (Ahrens et al. 2005; Martín‐Carratalá et al. 1998; Piscopo et al. 2010), French (Ahrens et al. 2005; Piscopo et al. 2010), Australian (Ahrens et al. 2005) and Tunisian (Ahrens et al. 2005; Martín‐Carratalá et al. 1998) samples, almonds are characterized by high amounts of fat (42–57%), protein (19–23%), carbohydrates (20–27%), and fiber (11–15%), and low amounts of moisture (3–9%) and ash (2.5–4.5%). Almonds are also acknowledged for their minerals, vitamins, and polyphenols (Yada et al. 2011).

12.1.3 Major Components

The relevant compounds studied in almond are detailed in Table 12.1, as well as the specific methodologies applied in each case.

Table 12.1 Compounds (ordered alphabetically) analyzed in each of the nuts studied in this chapter.

Source Compounds Analysis method Reference
Almond Dietary fiber Gravimetry Yada et al. 2013
Ellagitannins; gallotannins HPLC‐DAD/FD Xie et al. 2012
Fatty acids GC‐FID Askin et al. 2007; Barreira et al. 2012a; Cherif et al. 2009; García‐López et al. 1996; Kodad et al. 2014; Madawala et al. 2012; Maguire et al. 2004; Martín‐Carratalá et al. 1998; Matthäus & Özcan 2009; Piscopo et al. 2010; Soler et al. 1988; Venkatachalam & Sathe 2006; Zhu et al. 2015
GC‐MS Di Stefano et al. 2014
Minerals ICP‐AES Prats‐Moya et al. 1997; Yada et al. 2013
AAS Saura‐Calixto & Cañellas 1982; Piscopo et al. 2010
Phenolic compounds LC‐DAD/FD
MALDI‐TOF‐MS		 Bartolomé et al. 2010
–
HPLC‐FD/MS Xie et al. 2012
Proteins Kjeldahl digestion Ahrens et al. 2005; Askin et al. 2007; Kumar & Sharma 2005; Sathe 1993; Venkatachalam & Sathe 2006
Sterols HPLC‐DAD Maguire et al. 2004
GC‐FID Cherif et al. 2009; Yada et al. 2013
GC‐MS Madawala et al. 2012
Stilbenes UHPLC‐MS Xie & Bolling 2014
Sugars Enzymatic kit Amrein et al. 2005
Spectrophotometry Venkatachalam & Sathe 2006
HPLC‐RI Balta et al. 2009; Barreira et al. 2010; Kazantzis et al. 2003
Tocopherols HPLC‐DAD/FD Barreira et al. 2012a; Kodad et al. 2011, 2014; López‐Ortiz et al. 2008; Maguire et al. 2004; Matthäus & Özcan 2009; Zhu et al. 2015
RP‐HPLC‐UV Kornsteiner et al. 2006
RP‐HPLC‐FD Di Stefano et al. 2014
Triacylglycerols HPLC‐ELSD Barreira et al. 2012a
HPLC‐RI Martín‐Carratalá et al. 1999; Prats‐Moya et al. 1999
Vitamin B complex Microbiological assay Daoud et al. 1977; Hoppner et al. 1994; Yada et al. 2013
HPLC Rizzolo et al. 1991
Fluorometry Yada et al. 2013
RP‐HPLC‐UV Vasconcelos et al. 2007
Chestnut Ascorbic acid HPLC‐UV Pereira‐Lorenzo et al. 2005
Carotenoids HPLC‐DAD Pereira‐Lorenzo et al. 2005
Fatty acids GC‐FID Barreira et al. 2009b, 2012b; Borges et al. 2007; Fernandes et al. 2011
Dietary fiber Gravimetry Barreira et al. 2009b, 2012b; Gonçalves et al. 2010; Vasconcelos et al. 2007
Minerals AAS Borges et al. 2008
ICP‐AES Pereira‐Lorenzo et al. 2005
Organic acids UFLC‐PDA Carocho et al. 2013
Spectrophotometry Gonçalves et al. 2010
HPLC‐UV Ribeiro et al. 2007
Phenolic compounds RP‐HPLC‐UV Gonçalves et al. 2010; Vasconcelos et al. 2007
Protein Kjeldahl digestion Barreira et al. 2009b, 2012b; Gonçalves et al. 2010
Starch SEM‐LFD Cruz et al. 2013
Spectrophotometry Correia et al. 2012; Demiate et al. 2001; Vasconcelos et al. 2007
Sugars PA Pereira‐Lorenzo et al. 2005
HPLC‐RI Barreira et al. 2010; Fernandes et al. 2011
HPLC‐ELSD Bernárdez et al. 2004
Tocopherols HPLC‐FD Fernandes et al. 2011; Pereira‐Lorenzo et al. 2005
HPLC‐DAD/FD Barreira et al. 2009a,b, 2012b
Triacylglycerols HPLC‐ELSD Barreira et al. 2009b, 2012b, 2013
Hazelnut Carotenoids HPLC‐UV Kornsteiner et al. 2006
Fatty acids GC‐FID Bignami et al. 2005; Botta et al. 1994; Ciemniewska‐Żytkiewicz et al. 2015; Köksal et al. 2006; Madawala et al. 2012; Oliveira et al. 2008; Parcerisa et al. 1998; Seyhan et al. 2007; Venkatachalam & Sathe 2006
GLC‐FID Amaral et al. 2006a; Parcerisa et al. 1998
Minerals AAS Açkurt et al. 1999; Alasalvar et al. 2009; Köksal et al. 2006; Seyhan et al. 2007
Organic acids HPLC‐UV Botta et al. 1994
Phenolic compounds HPLC‐DAD‐MS Jakopic et al. 2011; Slatnar et al. 2014
RP‐HPLC‐DAD‐MS Ciemniewska‐Żytkiewicz et al. 2015
HPLC‐PDA Shahidi et al. 2007
Proteins Kjeldahl digestion Köksal et al. 2006
Sterols GLC‐FID Alasalvar et al. 2009; Amaral et al. 2006a; Parcerisa et al. 1998
GC‐MS Ciemniewska‐Żytkiewicz et al. 2015; Madawala et al. 2012
Sugars Spectrophotometry Venkatachalam & Sathe 2006
Tocopherols GLC‐FID Parcerisa et al. 1998
RP‐HPLC‐UV Ciemniewska‐Żytkiewicz et al. 2015; Kornsteiner et al. 2006
HPLC‐PDA Alasalvar et al. 2009; Bignami et al. 2005; Köksal et al. 2006
Triacylglycerols HPLC‐ELSD Alasalvar et al. 2009; Amaral et al. 2006b
Vitamin B complex Microbiological assay Açkurt et al. 1999
HPLC‐PDA Köksal et al. 2006
Walnut Carotenoids HPLC‐DAD Abdallah et al. 2015
Fatty acids GC‐FID Amaral et al. 2003; Bouabdallah et al. 2014; Li et al. 2007; Madawala et al. 2012; Rabrenovic et al. 2008; Tapia et al. 2013; Verardo et al. 2009
Minerals AAS Lavedrine et al. 2000; Tapia et al. 2013
Phenolic compounds HPLC‐DAD Colaric et al. 2005
UHPLC‐DAD‐MS Slatnar et al. 2015
HPLC‐DAD/LTQ‐MS Regueiro et al. 2014
HSCCC‐ESI‐IT‐TOF‐MS Grace et al. 2014
NMR; ESI‐MS Zhang et al. 2009
CE‐ESI‐TOF‐MS Gómez‐Caravaca et al. 2008
MEKC Verardo et al. 2009
Proteins SDS‐PAGE Labuckas et al. 2014
Sterols GLC‐FID Abdallah et al. 2015; Amaral et al. 2003; Schwartz et al. 2008
GC‐MS Madawala et al. 2012; Verardo et al. 2009, 2013
Tocopherols HPLC‐FD Abdallah et al. 2015; Madawala et al. 2012; Schwartz et al. 2008; Verardo et al. 2013
HPLC/UV‐DAD/MS Miraliakbari & Shahidi 2008
HPLC‐UV Kornsteiner et al. 2006
HPLC‐PDA Li et al. 2007
GC‐FID Verardo et al. 2009, 2013
Triacylglycerols GC‐FID Bouabdallah et al. 2014
Volatile compounds GC‐MS Abdallah et al. 2015

AAS, atomic absorption spectrometry; AES, atomic emission spectrometry; CE, capillary electrophoresis; DAD, diode array detector; ELSD, evaporative light scattering detector; ESI, electrospray ionization; FD, fluorescence detector; FID, flame ionization detector; GC, gas chromatography; HPLC, high‐performance liquid chromatography; HSCCC, high‐speed counter‐current chromatography; ICP, inductively coupled plasma; IEC, ionic exchange chromatography; IT, ion trap; LC, liquid chromatography; LFD, large field detector; LTQ, linear ion trap; MALDI, matrix‐assisted laser desorption/ionization; MEKC, micellar electrokinetic chromatography; MS, mass spectrometry; NMR, nuclear magnetic resonance; PA, pulse amperometry; PAGE, polyacrylamide gel electrophoresis; PDA, photodiode array detection; RI, refractive index; RP, reverse phase; SDS, sodium dodecylsulfate; SEM, scanning electron microscopy; TOF, time of flight; UFLC, ultra‐fast liquid chromatography; UHPLC, ultra‐high performance liquid chromatography; UV, ultraviolet.

The most abundant fatty acids in almond oil are oleic acid (50.41–81.20%), linoleic acid (6.21–37.13%), palmitic acid (5.46–15.78%), stearic acid (0.80–3.83%), and palmitoleic acid (0.23–2.52%). Linolenic acid and myristic acid were also detected (Askin et al. 2007; Barreira et al. 2012a; Madawala et al. 2012; Zhu et al. 2015). The percentages of fatty acids are also reflected by the triacylglycerol profile, where OOO (30–55%) and OLO (16–3%) were the major molecules, followed by OLL (6–15%), OOP (5–13%), LOP (3–11%), SOO (0.4–4.0%), PLP (0.1–3.2%), LLP (0.4–2.8%), and POP (0.03–0.46%), (L, linoleoyl; O, oleoyl; P, palmitoyl; S, stearoyl) (Barreira et al. 2012a; Martín‐Carratalá et al. 1999; Prats‐Moya et al. 1999).

Regarding the protein content, which is usually calculated from the amount of total nitrogen by applying specific nitrogen‐to‐protein conversion factors, the dominant protein in almonds is a globulin named amandin, which contains 19.3% nitrogen, corresponding to a conversion factor of 5.18. The general factor of 6.25 used in protein calculations is based on a 16% nitrogen content of many common proteins; however, using this factor for almonds would overestimate the protein content (Yada et al. 2011). Concerning the amino acids profile, asparagine (Asn) is by far the most abundant in almond proteins (Amrein et al. 2005).

Among the carbohydrates present in almond, sugars, starch, and some sugar alcohols are the only ones that can be digested, absorbed, and metabolized by humans. Nevertheless, the nonstarch fraction might promote physiological effects that are beneficial for human health. These indigestible polysaccharides (e.g. cellulose, hemicelluloses, oligosaccharides, pectins, gums, waxes) are the main components of the well‐known dietary fiber (Yada et al. 2011). Sucrose was reported as the predominant sugar in almonds, ranging from 11.5 to 22.2 g/100 g dry weight (dw); other individual sugars were detected in minor concentrations: raffinose (0.71–2.11 g/100 g dw), glucose (0.42–1.30 g/100 g dw), maltose (0.29–1.30 g/100 g dw), and fructose (0.11–0.59 g/100 g dw) (Balta et al. 2009; Barreira et al. 2010).

12.1.4 Minor Components

Regarding the vitamins present in almond, most literature is focused on the content of tocopherols in the kernels. Vitamin E (α‐, β‐, γ‐, δ‐tocopherol and α‐, β‐, γ‐, δ‐tocotrienol) is only produced in plants, and is a strong antioxidant with a protective role in biological systems, besides having hypocholesterolemic, anticancer, and neuroprotective properties (Sen et al. 2007). Almonds are considered one of the richest food sources of α‐tocopherol (Barreira et al. 2012a), which is the most biologically active form of vitamin E, utilized in the human body preferentially to the other forms (Brigelius‐Flohé et al. 2002). The content in each of the vitamin E isoforms is highly dependent on the cultivar, maturity stage, and geographical origin, but typically detected vitamers include α‐tocopherol (8.0–38 mg/100 g dw), α‐tocotrienol (0.01–0.30 mg/100 g dw), β‐tocopherol (0.02–0.25 mg/100 g dw), γ‐tocopherol (0.08–2.1 mg/100 g dw), γ‐tocotrienol (0.11–0.24 mg/100 g dw), and δ‐tocotrienol (0.02–0.005 mg/100 g dw). Among the various tree nuts, almonds typically contain the most vitamin E (Barreira et al. 2012a; Kodad et al. 2011; Kornsteiner et al. 2006; Madawala et al. 2012; Maguire et al. 2004; Matthäus & Özcan 2009; Yada et al. 2011; Zhu et al. 2015), with two handfuls of almonds providing the average daily recommended dose (15 mg) (Institute of Medicine 2000).

Studies analyzing the water‐soluble vitamin content of almonds are much scarcer, but these nuts are generally recognized as a good source of riboflavin (vitamin B2) and other complex B vitamins such as thiamine, niacin, pyridoxine, pantothenic acid, folic acid (folate), and biotin (Yada et al. 2011).

Furthermore, almonds are one of the top 40 richest food sources of polyphenols (Pérez‐Jiménez et al. 2010), which are mainly present as proanthocyanidins, followed by hydrolyzable tannins, flavonoids, and phenolic acids (Bolling et al. 2011; Xie et al. 2012). Stilbenes are generally available in lower amounts, but these compounds obtained from the shikimate and phenylalanine/polymalonate pathways may also contribute to the health‐promoting potential of polyphenol‐rich foods, through antioxidant or phytoestrogen activities. In almond, polydatin (Figure 12.1) has been reported as the most abundant stilbene (Xie & Bolling 2014). Furthermore, polyphenols from almond proved to be bioavailable in humans as they were detected as phase II and microbial‐derived metabolites in plasma and urine samples (Bartolomé et al. 2010).

Chemical structure of polydatin.

Figure 12.1 Chemical structure of polydatin.

The mineral content of almond, as in other plants, may be affected by many environmental factors and agronomic practices including geographic location, soil composition, water source, irrigation, as well as components of fertilizers and other agronomic production enhancers. Mineral content can also be influenced by the plant species or the botanical component undergoing analysis. In the particular case of almond, the nearly 3% of ash includes mainly potassium (K) > phosphorus (P) > calcium (Ca) magnesium (Mg) >>> iron (Fe) > zinc (Zn) > manganese (Mn), selenium (Se) > sodium (Na) > copper (Cu) (Yada et al. 2011).

12.2 Castanea sativa Miller (Chestnut)

12.2.1 Botanical Aspects and Geographical Distribution

Castanea sativa Miller belongs to the Fagaceae family, which includes several ecologically and economically important species (Manos et al. 2001). Chestnuts are found in three major geographical areas: Asia (with predominance of C. crenata, C. molissima, C. seguinii, C. davidii, and C. henryi), North America (where C. dentata, C. pumila, C. floridana, C. ashei, C. alnifolia, and C. paucispina thrive) and Europe, where C. sativa is predominant (Bounous 2005). According to the Food and Agriculture Organization (FAO), worldwide chestnut production is estimated at about 1.1 million tons. Europe is responsible for about 12% of global production, with relevance for Italy and Portugal, corresponding to 4% and 3%, respectively (Barreira et al. 2010). Chestnut is an important food resource in several countries. In Europe, chestnut is regaining interest, with an increase in production area from 81 511 ha in 2005 to 87 521 ha in 2008 (Fernandes et al. 2011).

12.2.2 Main Applications and Nutritional Overview

Chestnut kernels are a highly appreciated seasonal nut in Mediterranean countries, being consumed fresh or cooked, with roasting, boiling or frying being the most common cooking methods. Although a highly perishable product, nowadays chestnuts can be found on the market all year round due to the availability of frozen and boiled frozen chestnuts. Other important chestnut products are available on the market, such as the highly appreciated “marrons glacés” and chestnut flour obtained by grinding dried chestnuts, used for valorization of small chestnuts or chestnuts with double embryos (Cruz et al. 2013).

Chestnuts have become increasingly important in human nutrition because of their nutrient composition and potential beneficial health effects, for example, as part of a gluten‐free diet in cases of celiac disease (Pazianas et al. 2005) and in reducing coronary heart disease and cancer rates (Sabaté et al. 2000). Chestnuts are rich in carbohydrates and are a good source of essential fatty acids (despite their low fat amounts) and minerals, also providing several vitamins and appreciable levels of fiber (Borges et al. 2008).

12.2.3 Major Components

On a fresh weight basis, the major component in chestnut is water, which generally accounts for more than 50% of its weight (Barreirra et al. 2012b). Starch is the predominant component of dry matter, which makes chestnuts an excellent source of starch, above potatoes or wheat (Borges et al. 2008).

Sugar profiles are typically characterized by three main sugars: fructose, glucose, and sucrose. The concentration of each sugar is highly dependent on the cultivar; sucrose was detected as 3.71–24.17 g/100 g dw, glucose varied between 0.96 and 6.81 g/100 g dw, while fructose was quantified between 0.57 and 5.32 g/100 g dw (Barreira et al. 2010, 2012b; Bernárdez et al. 2004).

Protein content is usually around 3% (2.2–3.1%), depending on cultivar and harvesting year (Barreira et al. 2009b, 2012b), mainly constituted by a total of 17 amino acids: cysteine (Cys), proline (Pro), L‐alanine (Ala), L‐aspartic acid (Asp) (the dominant molecule), glycine (Gly), L‐glutamic acid (Glu), arginine (Arg) and the essential amino acids: isoleucine (Ile), leucine (Leu), lysine (Lys), L‐histidine (His), L‐methionine (Met), L‐threonine (Thr), L‐phenylalanine (Phe), L‐tyrosine (Tyr), L‐serine (Ser), and L‐valine (Val). Asp is the major amino acid (≈1.0 g/100 g dw), closely followed by Glu (≈0.8 g/100 g dw), Leu and Ala (≈0.6 g/100 g dw) and Arg (≈0.5 g/100 g dw). In general, chestnuts are a good source of these compounds; however, amino acid profiles are not well balanced, with certain essential amino acids occurring in limited concentration when compared to FAO recommended levels (Borges et al. 2008).

12.2.4 Minor Components

In chestnuts, the fat content is very low, but the fatty acids profile reveals high predominance of unsaturated molecules: 10–20% saturated fatty acids (mainly palmitic acid, C16:0), 10–30% monounsaturated fatty acids (particularly oleic acid, C18:1), and 50–70% polyunsaturated fatty acids (especially linoleic acid, C18:2, and linolenic acid, C18:3) (Barreirra et al. 2012b; Borges et al. 2007; Fernandes et al. 2011). The composition of fatty acids is, as expected, reflected in the triacylglycerol profile: LLLn, LLL, OLLn, PLLn, OLL, PLL, OOL, POL, PLP, OOO, POO, and PPO (L, linoleoyl; Ln, linolenyl; O, oleoyl; P, palmitoyl) (Barreira et al. 2012b, 2013). Furthermore, chestnuts are cholesterol free and contain a high amount of vitamin C. Some phenolic compounds, particularly gallic acid and ellagic acid (predominant among hydrolyzable and condensed tannins), and organic acids (oxalic, cis‐aconitic, citric, ascorbic, malic, quinic, succinic, shikimic, and fumaric acids) are also noteworthy (Carocho et al. 2013; Gonçalves et al. 2010; Ribeiro et al. 2007; Vasconcelos et al. 2007). Regarding the possible vitamin E isoforms, chestnuts are particularly good sources of γ‐tocopherol (γ‐tocopherol 754–957 μg/100 g dw; γ‐tocotrienol 28–84 μg/100 g dw; δ‐tocopherol 39–66 μg/100 g dw; α‐tocopherol 4–20 μg/100 g dw; α‐tocotrienol 2–8 μg/100 g dw) (Barreira et al. 2009a, 2012b; Fernandes et al. 2011).

The mineral profile in chestnut is characterized by high contents of K (473–974 mg/100 g dw), P (104–148 mg/100 g dw), Mg (63–93 mg/100 g dw) and Ca (41–51 mg/100 g dw), and low amounts of Fe (5.3–10.9 mg/100 g dw), Mn (3.1–8.0 mg/100 g dw), Na (0.9–3.9 mg/100 g dw), Zn (1.4–3.1 mg/100 g dw) and Cu (1.3–2.7 mg/100 g dw) (Borges et al. 2008; Pereira‐Lorenzo et al. 2005). Concerning human nutritional aspects, chestnuts have an important mineral content. K, Mg, Fe, Mn, and Cu have many physiological functions: K is associated with fluid balance and volume, carbohydrate metabolism, protein synthesis, and nerve impulses; P has an important role in mineralization of bones and teeth, energy metabolism, absorption and transport of nutrients; Mg is important in nervous activity and muscle contraction (Diehl 2002).

Additional information regarding the chemical parameters analyzed in chestnuts can be seen in Table 12.1.

12.3 Corylus avellana L. (Hazelnut)

12.3.1 Botanical Aspects and Geographical Distribution

Hazelnut (Corylus avellana L.) belongs to the Betulaceae family and is a popular tree nut worldwide, mainly distributed on the coasts of the Black Sea region of Turkey, southern Europe, and in some areas of the US (Oregon and Washington). Hazelnut is also cultivated in other countries such as New Zealand, China, Azerbaijan, Chile, Iran, and Georgia, among others. Turkey is the world’s largest producer of hazelnuts, contributing ≈74% to total global production, followed by Italy (≈16%), the US (≈4%), and Spain (≈3%) (Seyhan et al. 2007).

Hazelnuts are among the most popular nuts worldwide, with a global production average of nearly 1 million tons (MT) per year (888 328 MT in 2010), on an unshelled basis (Ciemniewska‐Żytkiewicz et al. 2015).

12.3.2 Main Applications and Nutritional Overview

About 90% of the world crop is shelled and sold as kernels with the remaining 10% utilized in shell for fresh consumption. Besides providing desirable flavor and texture to various foods, hazelnuts can play an important role in human nutrition and health due to their high oil, protein, vitamin, and mineral content (Hosseinpour et al. 2013; Tapia et al. 2013).

Hazelnuts play a major role in human health due to their very special nutritional value. One hundred grams of hazelnuts provide 600–650 kcal, mainly due to the fat (43–73%), protein (10–25%), and carbohydrate (10–20%) content. Besides being consumed fresh, hazelnuts are also used as an ingredient in confectionery products and the chocolate industry, as raw materials for pastry, and also add flavor and texture to an increasing variety of sweet and savory food products such as bakery, cereal, and dessert formulations (Amaral et al. 2006a).

The kernels are commercialized mainly after roasting, which gives them a more intense flavor and a crisper texture. Roasted hazelnuts are usually employed for obtaining butter paste or snacks, and also as ingredients for many products (e.g. cookies, ice cream, breakfast cereals, cakes, chocolates, coffee, bread, liqueurs, and spreads) (Jakopic et al. 2011). Eighty percent of the hazelnut kernels are processed in chocolate manufacture, 15% in confectionery, biscuit and pastry manufacture, and 5% is consumed without any further processing (Jakopic et al. 2011).

12.3.3 Major Components

Hazelnuts are particularly valuable for their lipid content (Hosseinpour et al. 2013; Köksal et al. 2006; Parcerisa et al. 1998; Venkatachalam & Sathe 2006), with a recognized prevalence of monounsaturated fatty acids, primarily oleic acid, which may reach 80% of total fatty acids. After oleic acid, linoleic acid (10–20%) and plamitic acid (4–10%) are the most abundant fatty acids in hazelnut kernels (Amaral et al. 2006a; Köksal et al. 2006; Madawala et al. 2012; Oliveira et al. 2008; Parcerisa et al. 1998; Seyhan et al. 2007). The lipid fraction is composed of nonpolar (98.8%) and polar (1.2%) constituents. Triacylglycerols are the major nonpolar lipid class, representing nearly 100% of the total nonpolar lipids in hazelnut oil. The main form in hazelnuts is OOO (71–78%), followed by PLL (10–13%), and POO (7.4–11%); other triacylglycerols detected in minor quantities were LLL, OLL, PLL, POL, PPL, PPO, SOO, and PSO (L, linoleoyl; O, oleoyl; P, palmitoyl; S, steareoyl) (Alasalvar et al. 2003, 2009; Amaral et al. 2006b).

Regarding their protein content, the corresponding amino acids profiles are also noteworthy, with predominance of Glu (2196–3475 mg/100 g) and relevant quantities (400–1000 mg/100 g) of Ala, Asp, Gly, Pro, Ser, and Tyr (Köksal et al. 2006).

12.3.4 Minor Components

Hazelnuts are also recognized for their high content of tocopherols, particularly α‐tocopherol (19–24 mg/100 g dw), and lower levels of the β (0.6–0.9 mg/100 g dw) and γ (1.3–2.3 mg/100 g dw) isoforms; and sterols, with predominance of β‐sitosterol (107–126 mg/100 g dw), high content of campesterol (6.7–8.9 mg/100 g dw), stigmasterol (0.7–0.9 mg/100 g dw) and Δ5‐avenasterol (5.1–6.1 mg/100 g dw) and lower levels of cholesterol (0.3–0.9 mg/100 g dw), chlerosterol (0.7–1.2 mg/100 g dw), β‐sitostanol (4.4–6.2 mg/100 g dw), Δ7‐stigmastanol (0.21–0.35 mg/100 g dw), campestanol (1.4 mg/100 g dw), fucosterol (0.4–0.6 mg/100 g dw), and Δ7‐avenasterol (0.9–1.3 mg/100 g dw) (Alasalvar et al. 2003, 2009; Amaral et al. 2006a; Ciemniewska‐Żytkiewicz et al. 2015; Köksal et al. 2006; Kornsteiner et al. 2006; Madawala et al. 2012; Parcerisa et al. 1998). Hazelnuts also contain dietary fiber as well as other beneficial nutrients, such as plant proteins, essential minerals, B complex vitamins, and phenolic compounds (Bignami et al. 2005; Köksal et al. 2006; Kornsteiner et al. 2006).

Besides their rich mineral content, in which K is prevalent (382–1470 mg/100 g dw), followed by P (202–708 mg/100 g dw), Ca (65–401 mg/100 g dw), Mg (35–310 mg/100 g dw), Mn (2.2–19.0 mg/100 g dw), Fe (3.0–5.0 mg/100 g dw), Zn (1.3–4.4 mg/100 g dw), Na (1.2–3.8 mg/100 g dw), Cu (0.9–3.2 mg/100 g dw), chromium (Cr) (10–18 μg/100 g dw), Se (5.5–8.1 mg/100 g dw), and molybdenum (Mo) (2.1–3.8 mg/100 g dw), hazelnut kernels are a valuable source of essential vitamins, such as vitamins B1, B6 and niacin (Alasalvar et al. 2009; Köksal et al. 2006; Seyhan et al. 2007).

Several studies characterizing phenolic profiles have been performed (see Table 12.1), revealing significant content of phenolic acids and flavonoids. Several compounds, such as gallic, caffeic, p‐coumaric, ferulic, sinapic, caffeoyltartaric and caffeoylquinic acids, procyanidins, catechin, epicatechin, glansreginins (Figure 12.2), and phloretins (Figure 12.3), have been quantified in hazelnut samples by several authors (Ciemniewska‐Żytkiewicz et al. 2015; Jakopic et al. 2011; Shahidi et al. 2007; Slatnar et al. 2014). Phenolics in hazelnut kernels protect the seed against oxidation and are associated with the moderate astringency and characteristic bitter taste of fresh nuts (Slatnar et al. 2014).

Chemical structure of glansreginin A.

Figure 12.2 Chemical structure of glansreginin A.

Chemical structure of phloretin.

Figure 12.3 Basic structure of phloretin.

Hazelnuts also contain organic acids, but in small quantities, with malic acid as the most abundant compound (Botta et al. 1994).

12.4 Juglans regia L. (Walnut)

12.4.1 Botanical Aspects and Geographical Distribution

Walnut (Juglans regia L.), which belongs to the Juglandaceae family, is a common nut in Mediterranean diets. Originating from Central Asia, the walnut is among the oldest cultivated fruit species. It is commercially planted throughout southern Europe, northern Africa, eastern Asia, the USA, and western South America. The 2012 world production of in‐shell walnut was above 3 400 000 tons (FAO 2013). Recently, walnut has been considered as a natural functional food of high economic interest due to its nutritional and medicinal benefits (Bouabdallah et al. 2014; Martínez et al. 2010).

12.4.2 Main Applications and Nutritional Overview

Walnut is a crop of high economic interest to the food industry. The edible part of the nut (the seed or kernel) is consumed fresh or roasted, alone or in other processed products. It is a nutrient‐rich food mainly due to its high fat and protein content but also contains many vitamins and minerals. The kernel represents between 40% and 60% of the in‐shell nut weight. It contains high levels of oil, 52–72%, up to 24% of proteins (usually 13–17%), 1.5–2% of fiber, and 1.7–2% of ash, depending on the cultivar, geographical location, and irrigation rate (Amaral et al. 2003; Martinez et al. 2006; Prasad 2003).

12.4.3 Major Components

Walnut proteins are highly digestible and have a good balance of essential amino acids. The major protein fraction is glutelins (≈70%), followed by globulins (≈18%), albumins (≈7%), and prolamins (≈5%) (Labuckas et al. 2014; Sze‐Tao & Sathe 2000). The most frequent amino acids in walnut proteins are Arg, Glu, and Ala, but several others are also found, such as Asp, Asn, Ser, glutamine (Gln), Gly, His, Thr, L‐citrulline (Cit), γ‐aminobutyric acid (GABA), Tyr, Val, Met, tryptophan (Trp), Phe, ornithine (Orn), Ile, Lys, Leu, and Pro (Mapelli et al. 2001).

Walnuts contain other beneficial compounds, such as polyunsaturated fatty acids (particularly linoleic acid: 57–66%, oleic acid: 13–24%, linolenic acid: 8–16%, and palmitic acid: 6–11%) and minerals (Bouabdallah et al. 2014; Li et al. 2007; Rabrenovic et al. 2008; Verardo et al. 2009). The triacylglycerol profile is characterized by four major molecules: LLLn, LLL, OLL and PLL, but several others were also detected (LLnLn, OLLn, SLL, OOL, SOL, OOO, SLS, SOO, PLLn, POL, PLS, POO, POS, PLP, and POP) (L, linoleoyl; Ln, linolenyl: O, oleoyl; P, palmitoyl; S, steareoyl) (Bouabdallah et al. 2014).

12.4.4 Minor Components

Tocopherols in walnut kernels are dominated by γ‐tocopherol (12–39 mg/100 g dw), followed by δ‐ (1.1–4.6 mg/100 g), α‐ (0.2–6.6 mg/100 g), and β‐isoforms (0.03–0.32 mg/100 g) (Abdallah et al. 2015; Kornsteiner et al. 2006; Li et al. 2007; Madawala et al. 2012; Miraliakbari & Shahidi 2008; Verardo et al. 2009). The predominant sterol is, by a high margin, β‐sitosterol (97–176 mg/100 g), followed by campesterol (0.5–8.8 mg/100 g), Δ5‐avenasterol (0.5–8.0 mg/100 g), and Δ5,24‐stigmastadienol (0.8–4.6 mg/100 g). Other detected sterols were cholesterol, brassicasterol, β‐sitostanol, Δ7‐campesterol, stigmastanol, Δ5,23‐stigmastadienol, Δ7‐stigmastanol, campestanol, stigmasterol, chlenosterol, and Δ7‐avenasterol (Abdallah et al. 2015; Amaral et al. 2003; Madawala et al. 2012; Schwartz et al. 2008; Verardo et al. 2009).

β‐Carotene is the major carotenoid (0.022–0.062 mg/100 g dw), despite the presence of other compounds such as β‐cryptoxanthin, lutein, zeaxanthin, violaxanthin, and neoxanthin (Abdallah et al. 2015).

The main phenolic compounds in walnut are phenolic acids (chlorogenic, caffeic, ferulic, p‐coumaric, sinapic, ellagic, and syringic acid), syringaldehyde and juglone (Colaric et al. 2005; Zhang et al. 2009), besides several hydrolyzable tannins and different flavonoids (especially vescalagin) (Fukuda et al. 2003; Slatnar et al. 2015; Verardo et al. 2009). Recently, more than 120 phenolic compounds, including hydrolyzable and condensed tannins, flavonoids and phenolic acids, have been identified or tentatively characterized in different walnut cultivars (Grace et al. 2014; Regueiro et al. 2014).

Walnuts are also characterized by high levels of K (300–487 mg/100 g), Mg (129–443 mg/100 g dw), P (308–385 mg/100 g dw), and Ca (58–135 mg/100 g dw) and, in contrast, very low levels of Na (0.3–6.7 mg/100 g dw), Mn (1.1–4.3 mg/100 g dw), Fe (1.5–2.9 mg/100 g dw), Cu (0.7–2.0 mg/100 g dw), Zn (1.2–1.9 mg/100 g dw), and Se (0.7–1.1 μg/100 g dw) (Lavedrine et al. 2000; Tapia et al. 2013).

In all these examples, laboratory determinations were achieved by applying several methodologies (see Table 12.1).

12.5 Conclusion

Nut consumption as part of a balanced diet is recommended. Clinical and preclinical trials have demonstrated that nuts have antioxidant, antidiabetic, and hypocholesterolemic actions (Xie & Bolling 2014). Furthermore, their consumption may improve body weight control and reduce the risk of obesity‐related diseases such as coronary heart disease and type 2 diabetes. In addition to cardiovascular benefits, which are mainly due to the lipids present in many types of nuts, other components might have important protective roles against the onset of several diseases.

Given the described profiles of different phytochemicals, it is also advised to consume a high variability of nuts, since their potential effects are often complementary, in relation to their different compositions of major and minor components.

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