“BIOPRESERVATIVE AGENTS FOR FRESH VEGETABLES”

ALEJANDRA G. PONCE, ; MARÍA R. MOREIRA ; AND SARA I. ROURA

Bioactive Natural Products

Indian Institute of Integrative Medicine

Año: 2010;

In the processing of vegetables is crucial that proper measures are taken to ensure the safety and stability of the product during its whole shelf life. Consumer demand for less use of synthetic preservatives has led to research and use of “naturally derived” antimicrobials. Biopreservatives effects are reducing or eliminating survival pathogenic bacteria, and increasing overall food products quality. Many naturally occurring compounds found in plants, herbs and spices have been shown to have antimicrobial function and serve as source of antimicrobial agents against foodborne pathogens. Most studies have evaluated the antimicrobial activity of naturally occurring botanicals on in vitro experiments. In a previous work, we analyzed the in vitro antimicrobial effects of ten essential oils, determining the MIC (Minimal Inhibitory Concentration) and reporting that clove and tea tree had inhibitory effects on E. coli using the Agar Diffusion Method. The effectiveness of essential oils application in food systems is the result of multiple factor associations such as composition and storage temperatures. Higher concentrations are needed to achieve the same effects in foods systems, taking into account the sensorial acceptability of the products. In this review we report the effectiveness of clove and tea tree application to control Escherichia coli O157: H7 on food such as blanched spinach and minced cooked beef exposed at abusive temperatures (8 and 20 °C). The antimicrobial action of clove and tea tree was dependent of the oil concentration, the food composition and the storage temperature. Preliminary findings in actual foods suggest that clove and tea tree oils could be used as potential natural biopreservatives capable of controlling food borne pathogens when foods are exposed to abusive temperatures, without adversely affects the sensorial acceptability of foods.             The use of edible films and coatings in food protection and preservation has recently increased since they offer several advantages over synthetic materials, such as being biodegradable and environmentally friendly. The antimicrobials imbedded in these films can be gradually released on the food surface, therefore, requiring smaller amounts to achieve the target shelf life. We studied the use of edible coating enriched with oleoresins, evaluating the susceptibility of the native microflora of butternut squash and L. monocytogenes analyzed by in vitro assays using a) film-forming solutions (chitosan, carboxymethyl cellulose and casein), b) oleoresins and c) film-forming solutions enriched with oleoresins. Film-forming solutions by themselves did not show significant antimicrobial properties. The oleoresins with meaningful antimicrobial activity against both squash native microflora and L. monocytogenes were olive and rosemary. Antioxidant properties were measured in vitro on different crude vegetable extracts. The enzyme source proved to affect peroxidase (POD) and polyphenoloxidase (PPO) susceptibility to the film-forming solutions. Most oleoresins significantly affected POD activity, regardless of the enzyme source. When the film-forming solutions were enriched with oleoresins, the latter lost, or retained their potential to reduce POD and PPO activities. In vivo experiments were focused on the treatments offering potential antibacterial and antioxidant benefits. The use of chitosan coatings enriched with rosemary and olive oleoresins applied to butternut squash did not produce a significant antimicrobial effect, however antioxidant effects were observed during the first day, exerting POD inhibition for up to 5 d of storage. Both oleoresins and chitosan enriched with these exerted significant antioxidant activities over PPO throughout 5 d of storage. Chitosan enriched with rosemary and olive improved the antioxidant protection of the minimally processed squash offering a great advantage in the prevention of browning reactions and did not introduce deleterious effects on the sensorial acceptability of squash.             Lactic Acid Bacteria (LAB) are useful preservation technologies and have long been used as starter cultures for foods and beverages fermentation for their contribution to flavor and aroma development and spoilage retardation. Their preservative effect is not only due to acidic conditions that these bacteria create in foods, but also their capacity for producing and excreting inhibitory substances. We characterized strains of (LAB) from organic vegetables. Genetic identification of selected LAB was performed by means of PCR method. These strains were Enterococcus faecium, Lactococcus lactis, Enterococcus hirae and Enterococcus canis. The antimicrobial activity of LAB strains was inactivated by the addition of proteases, thus confirming the proteinaceous nature of the inhibition. Bacteriocin-like substances were active against Gram-positive bacteria and Gram-negative foodborne pathogens, (Listeria monocytogenes and Escherichia coli), respectively. In all four strains the bacteriocin activity was stable after extend refrigerated storage and freezing-thawing cycles. This fact suggests that bacteriocin produced by the four LAB strains may find application as biopreservatives in minimally processed vegetables.                  These knowledges would make it possible to use these natural preservatives as emergent technologies to assist in preservation of foods by natural means.