Effect of plant biostimulants on nutritional and chemical profiles of almond [Prunus dulcis (Miller) D. A. Webb] fruit and potential application in functional foods
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The increasing interest in natural foods with functional effects requires ever-higher levels of production. Dried fruits are an example of this, since they are a relevant source of bioactive constituents. Almond [Prunus dulcis (Miller) D.A. Webb] is one of the most popular nuts in the world, standing out in the first place in what production level concern. 1,2 The benefits of including this nut in the human diet are partly related to its content on monounsaturated fatty acids (MUFA), particularly oleic acid, and polyunsaturated fatty acids (PUFA), namely linoleic acid, tocopherols (e.g., α-tocopherol) and phytosterols (e.g., β-sitosterol). 3,4 Nonetheless, the high production levels generates a global concern towards an agriculture less harmful to the environment, which raises the need for ecological alternatives to the use of conventional fertilizers and pesticides.5,6 Plant biostimulants, a class of bio-based agriculture products designed to improve crop development, might be used in agricultural fields to replace or reduce chemical fertilizers. In the study reported herein, different plant biostimulants compatible with organic farming (Fitoalgas Green®, a seaweed extract of Ascophyllum nodosum, Sprint Plus®, an amino acid-rich foliar spray, and Tradebor®, a boron fertilizer for soil and foliar application) were tested on almond orchards of the NE of Portugal. After field-treatments and collection, the nut samples were analysed for their nutritional value, fatty acids profile and tocopherols content.
The nutritional evaluation showed that almond nut is mainly composed of fat (around 55% on a fresh weight basis), which reached maximum values in the untreated control, with slight differences resulting from using different plant biostimulants. For protein levels, values close to 15 g/100 g fw were obtained. Ash and water, the minor components, showed minimal variations, each representing about 3 g/100 g fw. In what concerns energy, the maximal value (669 kcal/100 g fw) was obtained in the control treatment.
Sucrose was the only identified soluble sugar, with an average content of approximately 12 g/100 g fw. Tradebor treatments induced a higher sucrose content (13 g/100 g fw). As a general rule, low levels of monosaccharides (fructose and glucose, for example) in nuts serve as an indicator of the good storage conditions of the products.7
Regarding fatty acids, oleic acid (C18: 1n9c) was the predominant one (close to 70%), and its content remained almost unchanged in almond despite using different plant biostimulants. The lack of significant changes in almond was also observed for linoleic acid (C18:2n6c), which was detected up to 16%. The following fatty acids were palmitic acid (C16:0), with percentages close to 8.5%, and stearic acid (C18: 0), with values of approximately 2%. Other fatty acids were detected in trace percentages (total sum was less than 2%): myristic acid (C14:0), palmitoleic acid (C16:1), marginal acid (C17:0), α- linolenic (C18:3n3), eicosanoic acid (C20:0) and eicosenoic acid (C20:1), but without significant differences between fertilizer treatments. As in most foods with high-fat content, the concentration of tocopherols was elevated: average values of 50 mg/100 g fw, which is in agreement with previous reports. 8,9 Considering the concentration in total tocopherols, Fitoalgas Green® induced an increase of around 10% (50 to 55 mg/100 g fw), mainly due to the rise in α-tocopherol and γ- tocopherol. Nonetheless, all other assayed biostimulants had the opposite effect. Overall, the most notorious effects in almond samples were obtained with Fitoalgas Green®, particularly reflected in the upraising around 10% of γ-tocopherol and β-tocopherol contents.
Due to the high levels of α-tocopherol in almonds, consuming these products, besides being enjoyable, may also have important benefits because they can significantly increase the levels of dietary vitamin E.10
These results are important to help selecting the best plant biostimulant to be applied to increase the expression of a specific bioactive compound, adding greater commercial value to these products and enabling a potential application in functional foods.
