The intriguing notion that nut consumption could have a positive impact on human health has garnered widespread attention and exploration. Consequently, nuts are frequently advocated for their health benefits. Over the past few decades, an increasing body of research suggests a correlation between nut consumption and a lowered risk of major chronic diseases. Nuts, rich in dietary fiber, are associated with a decreased incidence of obesity and cardiovascular issues. Moreover, nuts contribute essential minerals, vitamins, and phytochemicals acting as antioxidants, anti-inflammatory agents, phytoestrogens, and other protective factors to the diet.
Presently, consumers prioritize achieving a diverse and balanced diet, leading to a notable uptick in incorporating nuts. This trend is fueled by the growing awareness of nuts’ distinct nutritional value, unique taste, flavor, and the presence of healthful bioactive compounds, including high-quality proteins, fibers, minerals, tocopherols, and phytosterols.
Nuts, typically categorized as dry fruits with edible seeds and tough shells, encompass cashews, walnuts, almonds, chestnuts, pistachios, and hazelnuts, with higher global production. They serve as a rich source of nutrients, featuring monounsaturated and polyunsaturated fatty acids, vitamins E and K, essential minerals like magnesium, copper, potassium, and selenium, dietary fiber, carotenoids, and antioxidant potential from phytosterols.
The convenience of transport, owing to their size, makes nuts suitable for various situations. Moreover, nut consumption is frequently linked to reduced risk factors for chronic diseases, attributed to their profile of fatty acids, squalene, fibers, plant proteins, minerals, vitamins, carotenoids, and phytosterols with potential antioxidant effects.
Interestingly, in certain nuts like almonds and peanuts, a significant portion of antioxidants resides in the skin, lost when removed. Similarly, cracking the hard shell of pistachios results in the loss of a substantial portion of antioxidants.
Nuts stand out as a substantial source of proteins and essential amino acids, primarily composed of seed storage proteins. Notably, nut allergies, excluding chestnuts, can trigger adverse reactions in some individuals. Various protein families contribute to nut allergies, with key players being 2S albumins, globulins (legumins and vicilins), non-specific lipid transfer proteins (nsLTP), plant pathogenicity-related proteins (PR-10), profilins, and oleosins.
Amendin, a legume protein, dominates almonds, while hazelnuts feature PR-10 Cor a 1 as the major allergen. Walnuts commonly contain legume Ju r 4 as the primary allergen. Pecans and pistachios showcase Albumin 2S Car I 1 and Pis v 1, respectively, as predominant proteins. Cashews, peanuts, and macadamia nuts present Ana o 1, Ara h 1, and Mac Ii 1 vicilins as the most prevalent allergens in their respective compositions.
The amino acid profile of nuts exhibits notable variation in both essential and non-essential amino acids. Hydrophobic amino acids dominate nut protein composition, followed by acidic, basic, and hydrophilic amino acids. Among non-essential amino acids, glutamic acid is paramount, ranging from 0.02 g/100 g in chestnuts to 6.20 g/100 g in almonds. Arginine, the second major non-essential amino acid, varies from 0.13 g/100 g in chestnuts to 3.10 g/100 g in peanuts, while aspartic acid ranges from 0.05 g/100 g in chestnuts to 3.15 g/100 g in peanuts.
Leucine takes precedence as the most essential amino acid, followed by phenylalanine and valine. Chestnuts have the lowest amounts of these essential amino acids (0.10, 0.07, and 0.09 g/100 g for leucine, phenylalanine, and valine, respectively), with peanuts being the richest sources of leucine and phenylalanine, and pistachios excelling as the richest source of valine.
Although the amino acid profile may vary with variety and location, hazelnut studies in Northeast China with 22 samples indicate consistent dominance of the same non-essential and essential amino acids (glutamic acid, arginine, aspartic acid, and leucine). This composition significantly influences various nut properties, including flavor, aroma, and color.
The nutritional value of food protein is influenced by the essential amino acid content and their digestibility. While nut proteins are often deemed incomplete compared to animal proteins, lacking all essential amino acids, their consumption is strongly linked to cardiovascular health. Notably, the substantial presence of arginine in all tree nuts positively impacts immune response, inflammation, and cardiovascular function. Arginine plays a key role in mitigating the risk of cardiovascular diseases and supporting reproductive function.
To optimize the health benefits of nut consumption, combining different protein sources is recommended to ensure adequate levels of all essential amino acids. This strategic approach enhances the overall nutritional profile and complements the inherent strengths of nut proteins.
Vitamins play a crucial role in maintaining a balanced and healthy diet, and nuts contribute significantly to this nutritional spectrum. Nuts contain fat-soluble vitamins, including ascorbic acid, B1, B2, B3, and B6, along with antioxidants such as α-tocopherol (vitamin E). These components promote overall health, combat aging, enhance brain function, and contribute to healthy skin.
Vitamin C (ascorbic acid), present in nuts, serves as a vital antioxidant for human colon cells. The chemical composition of nuts determines their nutritional value, with walnuts, almonds, pine nuts, and hazelnuts standing out for their richness in vitamin E. Almonds, cashews, pistachios, walnuts, and peanuts are noteworthy sources of vitamin B. Pistachios and chestnuts, in particular, exhibit higher concentrations of folic acid, while chestnuts lead in vitamin C content among nuts. The diverse vitamin content underscores the varied and beneficial contributions of nuts to overall health.
Nuts serve as rich sources of essential minerals, notably magnesium and potassium. In recent years, increasing nut consumption has been advocated for its potential to enhance mineral intake, making it a considered and heart-healthy snack when consumed in moderation. Nuts play a significant role as dietary sources of copper and magnesium, minerals that may offer protection against coronary heart disease.
Pistachios and cashews, in particular, stand out for their relatively high potassium content. Most nuts provide a good amount of zinc and iron, with pine nuts, cashews, and almonds exhibiting higher levels than others. While nuts are not notably high in calcium overall, certain varieties such as almonds offer relatively better calcium content. This diverse mineral composition reinforces the nutritional value of nuts and their positive impact on heart health when included in a balanced diet.
The presence of dietary fiber in nuts contributes to their health-promoting properties, as evidenced by epidemiological and clinical studies. Consumption of dietary fiber has been associated with an inverse relationship with conditions such as obesity, type 2 diabetes, cancer, and cardiovascular diseases. Notably, among nuts, almonds stand out for having the highest fiber content, and this amount is influenced by their genotype, indicating a clear genetic effect on fiber levels in almonds. Including almonds in one’s diet can thus provide a significant dietary fiber boost, contributing to overall health and potentially mitigating the risk of various health conditions.
The influence of genotype on almond fiber content has been emphasized in various studies, showcasing a variation from 7% to 9.70% in blanched almonds. This variation suggests that almond skin significantly contributes to the fiber content, constituting approximately 60% of the total fiber.
Cashews, in contrast, have the lowest fiber content, consistently ranging from 3-4%. Chestnuts and cashews share a similar fiber content, both being good sources of dietary fiber. Hazelnuts typically contain between 6.5 and 9.7 grams of fiber per 100 grams, highlighting their substantial fiber contribution to a balanced diet. The diverse fiber profiles of these nuts underscore the importance of considering them as valuable sources of dietary fiber in nutrition.
Nuts are indeed rich in various nutrients, with notable differences between different types and even subtle variations among cultivars. The lipid content and fatty acid profile are particularly dynamic parameters that can vary significantly when discussing nut composition. Beyond the inherent differences between nut species, factors such as genotype play a crucial role in influencing the lipid content and its characteristics.
Recent studies highlight that genotype, along with environmental factors, is a key determinant causing changes in several compositional parameters of nuts, especially in fat content. Understanding the interplay between genotype and environment is essential for comprehending the nuances in nut composition. These findings underscore the complexity of nut nutrition and the importance of considering both genetic and environmental factors when evaluating and appreciating their nutritional profiles.
Hazelnuts are recognized for having one of the highest fat levels among nuts, exceeding 60%. The predominant type of fat in hazelnuts is monounsaturated fat (MUFA), constituting approximately 80% of the total fatty acid content. Oleic acid, a monounsaturated fatty acid, is the primary component of this unsaturated fat profile.
Polyunsaturated fatty acids (PUFA) represent the second major fraction in hazelnut oil, primarily due to the presence of linoleic acid. However, some studies indicate that saturated fatty acids (SFA) can constitute the second major group of fatty acids in hazelnuts, influenced by a higher content of palmitic acid. This complex fatty acid composition contributes to the overall nutritional profile of hazelnuts and underscores the importance of considering these nuances when evaluating their health benefits.
Pistachios, like many other nuts, are indeed rich in fat, with available studies indicating levels of about 50%. Following the pattern observed in other nuts, pistachio oil is notably high in monounsaturated fatty acids (MUFA). The primary component of this MUFA fraction is oleic acid, with a contribution from palmitoleic acid. The second most significant fraction, polyunsaturated fatty acids (PUFA), is mainly composed of linoleic acid.
In terms of saturated fatty acids (SFA), the smaller fraction is nearly entirely comprised of palmitic acid in pistachios. This detailed fatty acid composition contributes to the nutritional richness of pistachios and aligns with the broader understanding of the health benefits associated with the consumption of nuts.
Walnuts indeed boast a remarkably high fat content, with only hazelnuts surpassing them in moderate amounts. While the fat content typically falls within the range of 60%, significant variations have been observed, ranging from 50% to 80%. However, most studies consistently report fat values around 60%, with some fluctuations linked to the specific cultivar under investigation.
The predominant type of fat in walnuts is polyunsaturated fatty acids (PUFA), making them distinct in this regard. Linoleic and linolenic acids contribute to the high PUFA content, while monounsaturated fatty acids (MUFA) represent the second most important type of fatty acid. Oleic acid is the primary MUFA in walnuts. This unique fatty acid composition contributes to the nutritional richness of walnuts and underscores their role in providing essential fatty acids in the diet.
Phenolics are indeed present in nuts, contributing to the array of beneficial effects associated with nut consumption on human health. Numerous studies highlight these positive impacts, including cardioprotective, neuroprotective, antidiabetic, anti-inflammatory, and antioxidant properties. Nut consumption has been shown to enhance the lipoprotein profile of cells and positively influence gut microbiota.
These health benefits can be attributed to the presence of various compounds, including phenolics, as noted by Lamuel-Ravento and Onge. Similar to other crops, the profile and phenolic content of nuts exhibit significant variation, influenced by factors such as genotype, cultural practices, climatic conditions, stage of fruit ripening, storage, and post-harvest conditions. Recognizing these factors is crucial for understanding and harnessing the full spectrum of health-promoting properties present in nuts.
The diversity of phenolic compounds in various nuts contributes to their health-promoting properties. In almonds, the most abundant phenols include catechin, epicatechin, protocatechuic acid, ferulic acid, kaempferol, and isorhemantin. Chestnuts are rich in gallic acid, vanillic acid, syringic acid, catechin, and ellagic acid. Hazelnuts excel in catechin, epicatechin gallate, and gallic acid. Peanuts showcase p-hydroxybenzoic acid, p-coumaric acid, ferulic acid, and epicatechin as dominant phenolic compounds. Pistachios feature gallic acid, syringic acid, catechin, and epicatechin. Walnuts stand out with high amounts of chlorogenic, caffeic, p-coumaric, ferulic, ellagic, and syringic acids.
In general, all nuts are rich in phenolic acids and flavonoids, contributing to their collective health benefits. While anthocyanins are present in residual amounts, their overall impact may not be considered significant. Understanding the specific phenolic composition of each nut provides insights into their unique nutritional contributions.
Indeed, the various phenolic compounds present in nuts are associated with significant beneficial effects on human health. Growing consumer awareness of these positive impacts has contributed to increased nut consumption. Higher nut consumption has been linked to a reduction in the prevalence of high cholesterol, blood pressure, diabetes, and gallstones, largely attributed to the richness of nuts in phenolic compounds.
Research has shown that a combination of phenolics found in natural almond skin, particularly epicatechin and catechin, demonstrated the ability to inhibit the growth of Staphylococcus aureus. This suggests the potential use of almond skin extracts in developing new products for topical use. Moreover, almonds, hazelnuts, and walnuts have demonstrated neuroprotective effects against Alzheimer’s disease, attributed to their richness in tocopherols and phenols. These findings highlight the multifaceted health benefits associated with incorporating nuts into the diet.
The aromatic composition of nuts is intricately linked to geographical origin, thermal processing, and the presence of microorganisms. In almonds, aldehydes, particularly benzaldehyde with its characteristic bitter almond taste, are identified as the main volatiles. Terpenoids and substances derived from amino acids contribute to the aromatic profile, often as a result of fatty acid oxidation.
Processing, including thermal treatments, induces changes in both the number of compounds and the available chemical classes. Chinese and Ukrainian walnuts, for instance, exhibit high levels of lipid-derived volatiles from linoleic acid and α-linolenic acid breakdown. Chilean walnuts, on the other hand, contain elevated levels of alkylbenzenes. Pyrazines emerge as the primary aromatic compounds in peanuts, formed through thermally induced Maillard reactions. This phenomenon is not exclusive to peanuts and extends to other nuts like pistachios and hazelnuts.
The roasting process plays a pivotal role in making nuts commercially viable and valuable. It enhances marketability and improves sensory characteristics, underscoring its significance in the nut industry.
In hazelnuts, several aromatic active compounds, including 2-acetyl-1-pyrroline, 2-propionyl-1-pyrroline, 5-methyl-(E)-2-hepten-4-one (Fibertone), 2,3-diethyl-5-methylpyrazine, 3,5-dimethyl-2-ethylpyrazine, and 2-furfuryl thiol, serve as suitable odorant indicators for distinguishing different nut aromas. Specifically, achieving a roasted or nutty aroma in hazelnuts involves ensuring that both 5-methyl-(E)-2-heptan-4-one and 3-methyl-4-heptanone are present in quantities exceeding 450 µg/kg. Additionally, maintaining the sum of two 2-acyl-1-pyrroline and two pyrazines below 500 µg/kg is important to avoid an excessive roasted smell.
By carefully controlling specific parameters such as temperatures, roasting techniques, and roasting time, it is possible to tailor the aroma of hazelnuts to meet the desired characteristics for each variety. This precision in processing allows for the creation of distinctive hazelnut aromas that contribute to the overall sensory experience of the nuts.
One significant quality concern with nuts is the potential development of off-flavors attributed to the formation of oxidative degradation products. The presence of various volatile substances, particularly 1-pentanol, 1-hexanol, and hexanal, is associated with tastelessness, and their elevated levels are indicative of undesirable flavor development, often referred to as rancidity.
While phytochemicals in tree nuts contribute to various health benefits, the bioavailability of these compounds can be affected by processing steps. Nuts undergo different processing methods to produce various end products. Common processing steps include shelling, blanching, and roasting. Roasting, in particular, is widely used to preserve the quality and extend the shelf life of nuts. It’s essential to strike a balance in processing to maintain both the sensory appeal and nutritional benefits of nuts while mitigating the risk of off-flavors.
Nuts indeed serve as rich sources of bioactive compounds, including tocopherols, vitamins, and phenolic compounds, known for their health benefits. Understanding the diversity of these bioactive compounds throughout the fruit growth and ripening stages is crucial. However, there is a current lack of knowledge about how global environmental changes and innovative crop production technologies might influence tree physiology, impacting fruit yield and quality.
Future research endeavors should focus on developing species-specific strategies that enhance both fruit quality and nutritional properties without significantly compromising yield. This involves selecting high-yielding nut species and cultivars well adapted to different growing regions and anticipated climate conditions. By doing so, we can produce fruits with excellent quality and high consumer acceptance, ensuring that nuts continue to be valuable contributors to a nutritious and healthful diet.