Abstract
Rice lipids are usually stable in the intact spherosomes in the cell. However, lipid membrane destruction by phospholipase, physical injury or high temperature, initiates hydrolysis through the action of lipases. Control of microbial induced lipolysis of rice would benefit from an approach that provides simultaneous antimicrobial and antioxidation control. Therefore, propolis, a resinous hive product collected by honeybees, known to possess both antimicrobial and antioxidant properties, was used in this study to evaluate feasibility of using its derived volatiles to control microbial prevalence, while providing oxidative stability of lipids, in stored brown rice (Oryza sativa, hinohikari var). Specifically, the effect of volatiles from Propolis including polar extracts (AEPE), non-polar extracts (MCPEV and HEPEV) and crude samples (CRUPV), on rice lipids oxidation and fungal and bacterial prevalence were studied. The stabilization effectiveness on oleic, linoleic and palmitic acids in brown rice were CRUPV> AEPEV> MCPEV>HEPEV>control, in the order of strength. Following brown rice storage, the bacterial species of Bacillus genera were most predominant with Bacillus cereus persisting on samples of all the treatments. Moraxella osloensis, Pseudomonas oleovorans, Sphingomonas paucimobilis, Xanthomonas campestris, Curtobacterium citreum, Curtobacterium flaccumfaciens and Aerococcus viridans affected the samples discriminately. Penicillium species was the most dominant fungi and persisted in all the treatments. MCPEV and CRUPV treated samples indicated the lowest species infestation numbers. Milling of the treated and stored brown rice samples indicated that samples treated with MCPEV and CRUPV had less broken rice than control samples. Also, the MCPEV treated samples were whiter than the control samples. The findings from this study show that there is potential to use Propolis extracts to limit lipid oxidation and microbial prevalence on rice.
Highlights
Rice lipids, which consists mainly of triacylglycerols and occur in the spherosomes located in the aleurone cells and embryo, are mainly responsible for the deterioration of rice flavor
Detailed results on qualitative characterization of the propolis samples used in this article involving the analysis of the scavenging activity on DPPH free radical, antioxidant activity analysis through the β-carotene-linoleic acid system of assay [8] and the gas chromatograph mass spectrometer (GC/MS) qualitative analysis can be obtained in our previous report [5]
The changes occurring in the three major fatty acids related to rice were studied and their levels in the whole grain investigated during a 12 months storage period under various treatments with crude propolis (CRUPV) and its extracts (AEPEV, MCPEV, and HEPEV)
Summary
Rice lipids, which consists mainly of triacylglycerols and occur in the spherosomes located in the aleurone cells and embryo, are mainly responsible for the deterioration of rice flavor. Oxidation of the lipids degrades the organoleptic quality of the product, reduces its nutritional value, and products of the oxidation processes can participate in the aging of an organism and in the aetiology of cardiovascular diseases and cancer [1]. There is currently much interest in natural antioxidants, including polyphenols, isolated from plants [2]. Because of their natural occurrence and consumption with plants, they are fully accepted by consumers, contrary to synthetic antioxidants which may initiate disease. Much research is being conducted to find completely safe, naturally active substances that strongly inhibit degradation of lipids in food systems. Lipolytic behavior of some microorganisms associated with rice storage demand that any such antioxidant should provide antimicrobial and antioxidative activities simultaneously
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