Polyphenol Oxidase Inactivation by Microwave Oven and Its Effect on Phenolic Profile of Loquat (<i>Eriobotrya japonica</i>) Fruit

The objective of this research was investigated the effect of polyphenol oxidase microwave treatment on phenolic composition, antioxidant activity and microstructure of loquat fruit. Phenolic profile of methanolic extracts prepared from fresh, and microwave-treated samples were analyzed. Antioxidant activity was also evaluated by 2,2’-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS?+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH+) methods. In addition, polyphenol oxidase inactivation was carried out using a response surface methodology to establish the optimal conditions of treatment. The phenolic content of fresh mesocarp was 311 ± 0.60 mg gallic acid equivalents (GAE)/100g dry weight (DW) and that of microwave-treated mesocarp was 1230 ± 0.36 mg GAE/100g DW. Total phenolic content of water/ methanol extract significantly increases after microwave treatment rather than methanolic extract of fresh loquat. Five glycoside phenolics were identified by HPLC-DAD-MS as 3-caffeoylquinic acid, 3-p-coumaroylquinic acid, 5-caffeoylquinic acid and quercetin-3-O-sambubioside. Methanolic extract of microwave-treated mesocarp showed higher antioxidant activity than that of fresh mesocarp. Thus, polyphenol oxidase inactivation by microwave energy preserved the integrity of phenolic compounds as well as antioxidant activity in mesocarp extracts prepared from loquat fruit. It was also noted that phenolics were more abundant in the microwaved samples than in the fresh samples.

Microwave Dried Carrot Pomace as a Source of Fiber and Carotenoids

Carrot pomace is a major by-product obtained during the industrial juice extraction process, which is discarded contributing to environmental pollution. This residue is rich in fiber, and contains high amounts of carotenoids and phenolic compounds that could contribute to its application as functional ingredient, improving the quality of foods and helping to reduce the environmental problem. In this study, carrot pomace powders obtained by microwave or hot air drying were incorporated into cookies in order to improve their phytochemical content. Cookies were prepared using a traditional cookie recipe substituting 30% of the wheat flour for either of the carrot pomace powders. Fiber, carotenoids and phenolic compounds were determined;image analysis and acceptability of the cookies were also conducted. The substitution of 30% of wheat flour for carrot pomace powders increased 3.7 fold the total dietary fiber of cookies, from 7.13 g/100gto26.44 g/100g;accounting the 7.4% of fiber daily intake with the consumption of one cookie (7 g). A similar pattern was found in the content of carotenoids and phenolic compounds. Carrot pomace dried with microwaves had the highest amount of these bioactive compounds. β-carotene, epicatechin, gallic and ferulic acids were identified in cookies with microwave carrot pomace powder. The cookies incorporated with carrot pomace powders exhibited improved antioxidant properties because of the increase in the phytochemical content. Acceptable cookies with appealing orange color were obtained. The results indicated that the replacement of wheat flour for carrot pomace powders yielded dietary fiber enriched cookies with improved carotenoid content.

Hypolipidemic Activity of Microwave-Dehydrated Mango (<i>Mangifera indica</i>L.) Powder in Mice Fed a Hypercholesterolemic Diet

The effect of dietary supplementation with mango (Mangifera indica L.) powder obtained by microwave dehydration was studied in normal and hypercholesterolemic mice. The phenolic profiles in methanolic extracts and antioxidant activities were determined using high-performance liquid chromatography and DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,2'-azino-bis-3-ethyl-benzothiazoline-6-sulphonic acid) assays, respectively. The total phenolic content of microwave-dehydrated mango powder was 1451.7 ± 26.7 μggallic acid equivalents/g dry weight. The main phenolic compounds identified were gallic acid, epicatechin, ferulic acid, and catechin. The anti-oxidant activity was 14.6% higher in microwave-dehydrated mango powder than in conventional mango powder. Mice were fed a hypercholesterolemic diet (1 g cholesterol/100g over 7 days). The hypercholesterolemic mice whose diets were supplemented with microwave-dehydrated mango powder showed a significant decrease (P ≤ 0.05) in total serum cholesterol compared to the hypercholesterolemic mice and the mice fed with conventional dehydrated mango powder. We observed a significant increase (P ≤ 0.05) in HDL-c levels in the microwave-dehydrated mango powder group mice (12.4 ± 1.3 mmol/L) compared to the hypercholesterolemic group (8.6 ± 1.4 mmol/L) and the conventional-dehydrated mango powder group (10.9 ± 1.3 mmol/L). The mice provided with microwave-dehydrated mango powder had significantly lower (P ≤ 0.05) levels of serum LDL-c (36.0%) and total cholesterol (43.3%) compared to the mice in hypercholesterolemic group. Notably, the atherogenic index was 72% lower in the microwave-dehydrated mango powder group compared to the hypercholesterolemic group. These results suggest that the biocompounds, such as polyphenols and dietary fiber, found in mango pulp might improve the lipid profile in mice fed a hypercholesterolemic diet.

Protective Effect of Phenolic-Rich Extracts from Different Parts of <i>Opuntia joconostle</i>Fruit against Carbon Tetrachloride-Induced Oxidative Stress in Mice

Opuntia joconostle fruit is a rich source of biocompounds such as polyphenols including gallic, vanilic, 4-hidroxybenzoic, cafeic, and syringic acids, catechin, epicatechin, rutin, and vanillin, besides betalains. The objective of this research was to evaluate the effect of supplementation polyphenols-rich extracts from different parts of Opuntia joconostle against carbon tetrachloride-induced oxidative stress in a mouse model. The animals were treated orally with polyphenols-rich extracts at 50, 100 and 200 mg/kg BW for 30 consecutive days. On day 30th the mice received carbon tetrachloride (CCl4) as hepatoxic agent. Biochemical evaluations were carried out 24 h after induction of the oxidative stress. Data showed that methanolic extracts from different parts of Opuntia joconostle exerting protective effect against the CCl4-induced oxidative stress in mice. Histology examination revealed that the damage decreased in groups treated with polyphenols-rich extracts compared to the group that did not receive any treatment. Opuntia joconostle fruit contains many phenolic compounds, flavonoids and betalains. The protective effect of extracts may be related to the phenolic composition and also by a counteraction with other compounds, such as betalains and flavonoids that increase their antioxidant effect.