Effects of air frying and enzymatic oxidation on the phenolic content and antioxidant properties of lower grade yellow mustard seeds
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Date
2021-05-31
Authors
Imran, Afra
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Abstract
Lower grade yellow mustard meal (LGYMM), a by-product of the mustard seed milling process has potential as a value added product in food, feed, and agro-allied industries. The under-utilized by-product of mustard can be used for the efficient release and extraction of bioactive phenolic compounds. Heat treatment and enzymatic assisted extraction have been reported to efficiently extract the bioactive compounds from oilseeds. This thesis was focused on the effect of air frying at different temperature/ time combinations (120 -180 °C from 5 to 20 min) and enzymatic oxidation using horseradish peroxidase (HRP) and tyrosinase at different incubation times (0, 1, 1.5, 2, 5 and 18 h) on the phenolic profile of LGYMM and its antioxidant activities. For air frying, sinapine was the major phenolic compound and its concentration decreased significantly (p<0.05) with prolonged time. The concentration of most of the phenolic compounds significantly (p<0.05) decreased with increased temperature-time with an exception at 180 °C where three thermogenerative compounds were detected. The highest total flavonoid content TFC (3.96 ± 0.19 QE µmol/g) and antioxidant activity (57.13 ± 8.81% for DPPH and 58.14 ± 7.91% for ABTS) for air frying was observed for the extracts at 180 °C for 15 and 20 min. For enzymatic oxidation, sinapine and SA were the major sinapates in untreated (UT) and alkaline treated (AT) mustard meal, which decreased significantly (p<0.05) with prolonged incubation time and generated some unknown end products. The maximum total phenolic content, TFC and antioxidant potential of both HRP and tyrosinase were evaluated at 1 and 2 h of incubation for UT and AT meal with HRP and tyrosinase, respectively. The results of this study found SA and sinapine were efficiently converted to enzymatic and thermogenerative end products that have high antioxidant activity. Enzymatic oxidation proved to be a better extraction technique for the extraction of polyphenolic compounds as the extracts possess higher antioxidant activity than the air fried extracts (an increase of 28- 30% for DPPH and 20- 22% for ABTS assay).
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Keywords
Enzymatic oxidation, Air frying, Phenolic compounds, Sinapic acid derivatives, Lower grade yellow mustard meal