Study review
A review of composition studies of cultivated almonds: Macronutrients and micronutrients

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Abstract

Prunus dulcis, the cultivated sweet almond, has long been recognized as a source of nutrients in many traditional diets, and is increasingly promoted as a healthy snack and ingredient. This paper reviews the global research over the past 50 years that has contributed to knowledge on the composition and characterization of almond macronutrients and micronutrients, specifically the lipids and fatty acids, proteins and amino acids, carbohydrates (including dietary fiber), minerals and vitamins. Tables providing an overview of major macronutrient and micronutrient contents (range of means per 100 g) as reported for almonds grown in various production regions are presented. Considerable variability in lipid content has been reported within and among commercial varieties and breeding selections; total lipids range from 25 to 66 g/100 g almonds (fresh weight). Oleic and linoleic acids account for about 90% of total lipids, and saturated fatty acid levels are very low (<10%) in all varieties from all regions. However, oleic/linoleic acid ratios vary widely among varieties. Total protein contents range from 14 to 26 g/100 g almonds. α-Tocopherol is the major vitamin E isomer in all almond varieties assessed; β-, γ- and δ-tocopherols are minor components. Published data on total dietary fiber (TDF), minerals and other vitamins in almonds are limited.

Introduction

The cultivated sweet almond (Prunus dulcis) is a nutritionally important and valuable specialty crop grown in many temperate and sub-tropical regions in the world, both for domestic consumption and for trade. Almonds belong to the genus Prunus and the subgenus Amygdalus, within the Rosaceae family. The cultivated almond is designated as Prunus dulcis (Miller) D.A. Webb; listed synonyms include Prunus amygdalus Batsch and Prunus communis L. as well as the early designation Amygdalus communis L. (Kester et al., 1991, USDA, 2010c). The sweet or bitter flavor characteristic of almond kernels is an inherited trait (Dicenta and García, 1993). Bitter almonds contain significant amounts (3–9%) of amygdalin, a diglucoside, which releases hydrocyanic acid and benzaldehyde upon enzymatic hydrolysis (Wirthensohn et al., 2008); bitter almonds are used primarily in the production of flavor extracts. This review focuses on the sweet almond, which is the predominant type cultivated globally.

Sweet almonds have been cultivated for thousands of years and valued for both food and medicinal uses. Similar properties (such as “hot” or “heating,” “cleansing,” “nourishing,” “strengthening mental functions”) are ascribed to almonds in the ancient medical and scientific texts of the Greeks and then the Persians, and later in traditional Chinese medicine and Indian Ayurvedic medicine, indicating that ideas were exchanged and adapted as almonds were introduced from western to eastern Asia (Albala, 2009).

Almonds and other tree nuts, as well as peanuts, are nutrient-dense foods that can be a valuable plant source of lipids and protein in the diet (King et al., 2008). Over the last several decades, researchers have also identified that the contents of dietary fiber, vitamin E, phytosterols and several key micronutrients found in almonds and other nuts contribute to a healthy nutrient profile. Studies on the numerous health benefits of daily nut consumption, especially in relation to blood lipids, cardio-protective effects and metabolic health, have been extensively reviewed (e.g. Coates and Howe, 2007, Griel and Kris-Etherton, 2006, Jenkins et al., 2008, Richardson et al., 2009) and additional studies are ongoing. Emerging research on the potential prebiotic properties of almonds (Mandalari et al., 2008) and on almond skins as a rich source of bioactive polyphenols (Mandalari et al., 2010, Milbury et al., 2006, Monagas et al., 2007, Urpi-Sarda et al., 2009) is further enhancing the health profile of this nut.

Over a decade ago, Schirra (1997) compiled a comprehensive review on the postharvest technology and utilization of almonds that also included brief research summaries of the macronutrients and micronutrients in almond kernels. To our knowledge, no other review has been presented on macronutrient and micronutrient composition studies of almonds cultivated in various countries. Almond production, which requires a Mediterranean-type climate, is concentrated in four main regions: California (western United States [US]), the Mediterranean, central Asia, and Australia.

The major aim of this review was to compile the scientific literature available (in English) on the composition of natural, unblanched almonds and present an overview of the global research from the past 50 years on macronutrients and micronutrients in cultivated almonds. Only studies that clearly identified the production region or country of origin as well as the cultivar (variety) or local breeding selection of the almonds being analyzed were included. Also, sample numbers and analytical method(s) used had to be clearly described. The literature on the macronutrient and micronutrient composition of almonds is surprisingly limited, aside from lipid analyses, and few studies have thoroughly assessed different cultivars or varieties grown in various locations over a number of production years. This latter issue is critical especially in terms of the lipid content of almonds, which can vary significantly within cultivars and breeding selections harvested in different years. A compilation of the existing data may be a useful guide for nutritionists and nutrient database compilers as well as for further research studies.

Consumer, industrial and food service demand for almonds continues to rise globally, especially in emerging markets, such as China and India, and also in more traditional markets, such as Western Europe (ABC, 2010). Quality composition data are essential for nutrition researchers, health professionals and food labeling. Recent comparisons of nutrient values for natural almonds as cited in selected European and Asian national food composition tables (and presented as posters at international nutrient database conferences in 2009) revealed a wide range of macronutrient and micronutrient data, missing values, and compilations from sources that no longer represent the best available data (unpublished, available from author).

Thus, an additional aim of this review was to present some background to the updated and comprehensive nutrient data set now available for natural almonds in the United States Department of Agriculture (USDA) National Nutrient Database for Standard Reference (SR), Release 23 (SR23) (USDA, 2010a), and also to consider these nutrient values in relation to the available research. The US, specifically the state of California, accounts for about 80% of commercial almond production globally (on a shelled basis) (USDA, 2009a), and over two-thirds of the crop is exported annually to about 90 countries throughout the world (ABC, 2010). The need for representative composition data is underscored by the global availability and widespread consumption of this supply of almonds.

Section snippets

Lipids

The majority of almond composition research globally has focused on the lipid and fatty acid fractions. The lipids in almonds consist primarily of storage lipids, which are present as intracellular oil droplets (approximately 1–3 μm in diameter) in the cotyledon tissues of the kernels (Pascual-Albero et al., 1998, Ren et al., 2001). Almonds and many other edible tree nuts are a rich source of lipids composed predominantly of mono- and polyunsaturated fatty acids (USDA, 2010a, Venkatachalam and

Protein and amino acids

To calculate the protein content of almonds, the amount of total nitrogen (N) determined by analytical methods is most commonly multiplied by the specific nitrogen-to-protein conversion factor of 5.18 (EuroFIR, 2008, FAO, 1970, USDA, 2010a, USDA, 2010b). Many of the nitrogen-to-protein conversion factors commonly in use today are based on the original recommendations of Jones (1941) in a US Department of Agriculture review, and may be referred to as “Jones” factors. As cited by Jones (1941),

Carbohydrates

Sugars, starches and the nonstarch polysaccharides (cellulose, hemicelluloses, etc.) are the carbohydrates typically found in seeds and other plant tissues. Of these carbohydrates in almonds, only the sugars, starch and some sugar alcohols can be digested, absorbed and metabolized by humans to provide a source of energy. The nonstarch polysaccharides are indigestible and therefore unavailable as an energy source, but they promote physiological effects that are beneficial for human health.

Minerals

The minerals found in plant tissues, including seeds such as almonds, are obtained by the plant from the soil in which it grows and the water applied in production. Thus, the mineral content of plant tissues can be affected by many environmental factors and agronomic practices including the following: geographic location of plants or trees, soil composition, water source, irrigation, as well as components of fertilizers and other agronomic production aids. Mineral content can be influenced

Vitamins

The limited literature available on vitamins in almonds is primarily focused on the content of tocopherols in the lipid fraction of the kernels, and the effects of storage on tocopherol degradation. Tocopherols (α-, β-, γ-, δ-T) and tocotrienols (α-, β-, γ-, δ-T3) are compounds with differing vitamin E activity produced only in plants. It is well established that these eight different vitamin E isoforms are antioxidants and have protective roles in biological systems, and recent data indicate

National databases

National food composition databases strive to provide quality composition data to meet the diverse needs of users in such areas as clinical research, patient and consumer education, and product development and labeling. Data for food items may come from many sources, including the scientific literature. In recent comparisons of nutrient values for natural almonds as cited in selected European and Asian national food composition tables, we found a wide range in the availability of macronutrient

Conclusions

The nutrient composition of almonds is mainly genotype-dependent, and may also be influenced by environmental factors, such as growing region, cultivation methods, climatic conditions that vary between harvest years, and kernel maturity, or interactions of these factors. In addition, variability in the nutrient composition of almonds, even within a cultivar, can be expected because almonds are natural products. Future research into nutrient variability attributed to almond genotype, along with

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