Abstract
The drive towards sustainable food systems coupled with increased consumer sophistication have prompted innovation in waste valorization. Grape and citrus processing by-products, abundant in the Mediterranean and tropical regions, respectively, are expanding and are sustainable sources of bioactive phytochemicals that can be used as natural preservatives for foods. Phytochemical composition, antioxidant, and antimicrobial properties of extracts from grape pomace (GPE), seeds (GSE), and clementine mandarin peel and pulp (MPE) grown in South Africa were analyzed. Total phenols and carotenoids were highest in GPE followed by GSE and MPE (p ≤ 0.05). Flavonoids and anthocyanins were higher (p ≤ 0.05) in GPE and GSE compared to MPE. The GSE had the highest proanthocyanidins content followed by GPE and MPE (p ≤ 0.05). Ascorbic acid was only detected in MPE, which also had the highest titratable acidity and lowest pH values (p ≤ 0.05). The GSE had the highest antioxidant potency composite index followed by GPE and MPE (p ≤ 0.05). The order of antimicrobial activity of the extracts was MPE > GSE > GPE (p ≤ 0.05). Current findings show that GSE is a potential antioxidant while MPE holds promise as an antimicrobial for the food industry.
Highlights
About 1.6 billion tons of food are lost or wasted annually [1]
Folin-Ciocalteau reagent, sodium carbonate, aluminium chloride, dimethyl sulfoxide (DMSO), butylated hydroxytoluene (BHT), hexane, sodium nitrite, and sodium hydroxide (Merck, Darmstadt, Germany); the standards gallic acid, catechins, L-ascorbic acid, (±)-6-hydroxy-2,5,7,8tetramethylchromane-2-carboxylic acid (Trolox), and β-carotene, the reagents polyvinylpyrrolidone, 2,2-diphenyl-1-picryl-hydrazyl (DPPH), 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ), fluorescein sodium salt, 2,2 -azobis (2-methylpropionamidine) dihydrochloride (AAPH), sodium tetraborate, boric acid, xylenol orange, linoleic acid, 15-lipoxygenase enzyme, nordihydroguaiaretic acid (NDGA), Mueller-Hinton agar, Mueller Hinton broth, iodonitrotetrazolium chloride (INT), sodium metabisulphite, and tetracycline used in the current study were purchased from Sigma-Aldrich (Steinheim, Germany)
Total phenolic content was highest in grape pomace (GPE) with intermediate and lowest contents in GSE and mandarin peel and pulp (MPE), respectively (p ≤ 0.05)
Summary
About 1.6 billion tons of food are lost or wasted annually [1]. In South Africa, for example, annual postharvest food losses and wastes amount to 10 million tons [2], with about 95% of the food wastage occurring along the value chains prior to reaching the consumer. Cancer has historically been associated with nitrate and nitrites used in processed foods [5], while the use of benzoates has been linked to hyperactive behavior in children, allergies, asthma, and skin rashes [4,6,7]. Access of such information to the public influences their purchasing behavior towards trust and preference of foods preserved with natural preservatives [5,8]. These developments have prompted researchers to pursue natural preservatives mainly derived from plants, viewed as nutritious, safe, healthful, and promote sustainable food systems [3]
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