TITLE:
Polyphenol Oxidase Inactivation by Microwave Oven and Its Effect on Phenolic Profile of Loquat (Eriobotrya japonica) Fruit
AUTHORS:
Yanet Chávez-Reyes, Lidia Dorantes-Alvarez, Daniel Arrieta-Baez, Obed Osorio-Esquivel, Alicia Ortiz-Moreno
KEYWORDS:
Loquat; Phenolic Compounds; Polyphenol Oxidase; Microwave; Eriobotrya japonica
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.4 No.9B,
September
20,
2013
ABSTRACT: 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.