Abstract:
Dalmoth is a kind of snack, manufactured by deep frying process and most popular in Nepal, India and other south Asian countries. This traditional product is becoming an emerging industrial product. Different varieties of dalmoths are manufactured in industries. Although dalmoth is dry and low moisture food, it has a short shelf life. Lipid oxidation is one of the major problems of dalmoth during storage which leads to deterioration in shelf life, sensory quality and ultimately developing health hazardous compounds like free radicals, ketone and aldehydes. Therefore, this research was concentrated on retardation of lipid oxidation in one type of dalmoth, namely "mung dalmoth" by enrichment of banana peel extract (BPE) in frying oil during dalmoth preparation. Banana peel contains various antioxidant compounds such as gallocatechin, dopamine, tannins and phenolic compounds which protect fatty foods from lipid oxidation. This research aimed (1) to evaluate the total phenolic compounds, total flavonoids and antioxidant activities of BPE, (2) to investigate the effect of the BPE on stability of frying oil as well as storage stability of mung dalmoth and (3) to compare the effectiveness of BPE and synthetic antioxidant (BHA) on the stability of lipid oxidation of mung dalmoth during storage. The methodology was divided into four experiments: (1) preparation of banana peel extract, (2) determination of total phenolic content, flavonoids content and antioxidant activities of banana peel extract, (3) examination of the effect of BPE on stability of refined soybean oil during frying and (4) investigation of the chemical quality of mung dalmoth during storage at accelerated temperature for 60 days. The banana peel was extracted by a solvent extraction method (ethanol: water = 9:1) and total polyphenol, total flavonoids and antioxidant activities (DPPH and FRAP assay) were evaluated. During dalmoth preparation, frying oil was enriched with the BPE at different concentrations (0, 250, 500, 750 and 1000 ppm). BHA, a synthetic antioxidant was also used at 200 ppm to compare with banana peel extract treatment. To evaluate the effect of BPE on frying oil, chemical properties of oil (acid value, peroxide value, p-anisidine value and thiobarbituric reactive substance assay) were analyzed before and after the frying. The prepared mung dalmoth was stored at 30, 40 and 50ºC for 60 days to investigate the chemical properties (moisture content, peroxide value, free fatty acid, p-anisidine value, and thiobarbituric reactive substance assay) of mung dalmoth. These values were analyzed at the different time interval (0, 10, 20, 30, 40, 50, and 60 days) to determine the shelf life and to select the optimum concentration of BPE enrichment. Statistical analysis was carried out to establish any significant difference in the analyzed data.
The banana peel demonstrated the good source of natural antioxidant as it exhibited good source of phenolic content (8.03±0.51 mg gallic acid equivalent/g), total flavonoids content (8.71±0.30 mg of catechin equivalents (CE)/g) and antioxidant activity as DPPH scavenging activity (EC50 = 87.44 μg/ml) and FRAP (4.45±0.17 mM Fe2+/g). The BPE at 750 and 1,000 ppm level was the most effective in minimizing the peroxide value, free fatty acid, p-anisidine value and thiobarbituric acid reactive substance (TBARS) value of mung dalmoth during 60 days of storage at 30, 40 and 50°C than that of 200 ppm BHA. Descriptive results showed that higher levels BPE (750 and 1,000 ppm) prevented the rancidity development more effectively during storage whereas 250 and 500 ppm BPE showed the comparable efficiency with synthetic antioxidant BHA at 200 ppm.
The Q10 value for peroxide value of mung dalmoth samples ranged from 1.66 to 1.70 and the predicted shelf life of mung dalmoth at 25°C was 30, 38, 45, 50, 53 and 41 days for enrichment of BPE at 0, 250, 500, 750 and 1000 ppm and BHA at 200 ppm during frying process, respectively. Therefore, the banana peel extract has a great potential for use as natural antioxidants to preserve the mung dalmoth.
Mae Fah Luang University. Learning Resources and Educational Media Center