Antioxidants have been widely studied in the fields of biology, medicine, food, and nutrition sciences. There has been extensive work on developing assays for foods and biological systems. The scientific communities have well-accepted the effectiveness of endogenous antioxidants generated in the body. However, the health efficacy and the possible action of exogenous dietary antioxidants are still questionable. This may be attributed to several factors, including a lack of basic understanding of the interaction of exogenous antioxidants in the body, the lack of agreement of the different antioxidant assays, and the lack of specificity of the assays, which leads to an inability to relate specific dietary antioxidants to health outcomes. Hence, there is significant doubt regarding the relationship between dietary antioxidants to human health. In this review, we documented the variations in the current methodologies, their mechanisms, and the highly varying values for six common food substrates (fruits, vegetables, processed foods, grains, legumes, milk, and dairy-related products). Finally, we discuss the strengths and weaknesses of the antioxidant assays and examine the challenges in correlating the antioxidant activity of foods to human health.

Black carrot, which is an economically important product, is produced extensively in Konya and Hatay regions in Turkey. Kombucha tea is a symbiotic system, comprises of bacteria and yeasts cultures called as SCOBY, and produced by fermentation of sugar and tea leaves. Kombucha samples contained black carrot juice in two concentrations (10 and 20%) and compared with the Kombucha contained green tea leaves. Black carrot varieties were used for enrichment of Kombucha production and investigated in terms of physico-chemical properties and antioxidant capacity. Black carrot samples belonging to the Hatay region, have higher anthocyanin content (660.26 mg C3G/100 g-dw), antioxidant capacity (TEACABTS and TEACCUPRAC; 15.33 ± 0.39 and 21.91 ± 0.28 µmole Trolox/g), total phenolic content (67.22 ± 0.24 mg/g GAE) and bioaccessibility (36.48 ± 0.78 mg/g GAE) comparing to Hatay black carrot variety. The highest anthocyanin content (71.05 mg C3G/100 mL), antioxidant capacity (TEACABTS and TEACCUPRAC; 3.67 ± 0.15 and 12.33 ± 0.11 µmole Trolox/g) were obtained from Kombucha tea containing black carrot juice (20%). According to the sensorial evaluation, panelists stated that the Kombucha samples with Hatay Black carrot juice had a fresh and pleasant taste and flavor due to green tea aroma.

Graphical Abstract : TOC-Table of content. Abstract Spirulina produced in Turkey has a high antioxidant capacity determined by the three common methods (ABTS, CUPRAC, and DPPH). The major phenolics found in Spirulina were acacetin (53.62%) and pinocembrin (41.28%). The bio-accessibility values of the phenolic compounds in Spirulina were approximately 60%. PUFA’s are the significant antioxidant compounds to prevent lipid peroxidation. Spirulina has been found to reduce blood sugar and oxidative stress due probably to the high amount of ω-6 PUFA. By the treatment of Spirulina, the levels of antioxidant enzymes (GSH-Px and SOD) were increased 240 and 60% in the healthy rats, while 19 and 59% in the diabetics. In diabetic rats fed with Spirulina, glucose, triglyceride, total cholesterol levels in blood and malondialdehyde content in body tissues were decreased by 20, 31, 22 and up to 56%, respectively. In-vitro and in-vivo tests have shown that Spirulina has anti-hyperglycaemic, anti-hyperlipidaemia and antioxidative effects on diabetic rats.

Anthocyanins have a great potential for human health, as a sub-group of phenolic compounds. Interactions of anthocyanin involved in digestion and thus in obesity consist of inhibition of pancreatic lipase, regulation of lipolysis and lipogenesis, activation of an activated protein kinase enzyme, controlling of digestion hormones (leptin, insulin, ghrelin, cholecystokinin, GIP, GLP-1). Anthocyanins are the compounds that can control metabolic syndrome and obesity by ameliorating lipid metabolism, increasing energy expenditure, suppressing food intake and inhibiting lipid absorption. In addition, the interactions with other compounds during the processing and/or in the intestinal canal can change their absorption capability and bioavailability. Activation of mitogen-activated protein kinase and cyclooxygenase (COX) enzymes, inflammatory cytokines signaling, free-radical scavenging activity are among the primary functions of anthocyanins playing role in the basic metabolic pathways. Anthocyanins also interact with gut microbiota that plays a role in many metabolic pathways. In the review, the effects of anthocyanins on the obesity-associated mechanisms in the metabolism are considered and summarized under the light of recent researches.

Vinegar has been known as a traditional remedy since ancient times. In addition to being used as a flavoring and aroma enhancer in world cuisines, it has attracted more and more attention due to its bioactive potential and health properties. Although the most common use is apple cider vinegar together with grape vinegar, vinegar produced from red fruits has come to the fore due to their health purposes. Rosehip, pomegranate, fig, guelder-rose, blackberry, raspberry, and blueberry vinegars were evaluated regarding the organic acid content, phenolic compound content, and bioactive potential to assess their health potential and associated contents. Acetic acid, citric acid, succinic acid, and malic acid were determined as prominent organic acids in the vinegar samples. In contrast, gallic acid, vanillic acid, protocatechuic acid, and ferulic acid were dominant regarding phenolic compounds. Raspberry, guelder-rose, and pomegranate vinegars came forth regarding their bioactive content and potential. The discriminative parameters of the vinegar samples were pH, total acidity, dL-isocitric acid, gallic acid, and hydroxybenzoic acid. Fruit vinegars were determined to have a notable bioactive content compared to apple and grape vinegars. The use of these vulnerable bioactive materials in vinegar fermentation could provide an effective way for nutrition and raw material resourcing.