Statistical optimization of a novel low-cost medium based on regional agro-industrial by-products for the production of proteolytic enzymes by Bacillus cereus.

Bacillus sp. are specific producers of peptidase amongst bacteria and peptidase enzymes and are of significant ones due to their multifarious applications. Advances in industrial biotechnology offer potential opportunities for economic utilization of agro-industrial by-products for many biochemical reactions. Due to their rich organic nature, they can serve as an ideal substrate for the production of different value added products like peptidases. In the present work, an attempt was made to optimize different variables by Taguchi methodology for the production of peptidase using agro-industrial by-products hydrolyzed by a Bacillus cereus strain, resulting in brewer's spent grain (BSG) being the optimal organic substrate. Subsequently, operative variables for the BSG were investigated using Taguchi methodology in order to maximize the enzyme production. Additionally, the main medium components were optimized using a mixture design. Finally, the production of peptidase by B. cereus was investigated; also the possible interaction with other proteolytic microbial strains was evaluated. A notorious synergistic effect was observed when B. cereus was inoculated with Pseudomonas sp. These brought a triple benefit, first, opening the possibility to produce technical enzymes at low cost, second, giving greater value to a food industry by-product, and third, reducing the environmental impact caused by the product removal directly into the environment.

Postharvest changes in water status and chlorophyll content of lettuce (Lactuca sativa L.) and their relationship with overall visual quality.

The purpose of this study was to evaluate water status, chlorophyll content (C), and overall visual quality (OVQ) of fresh butter lettuce (Lactuca sativa var. Lores) as well as these indexes' evolution during storage and their relationships, if any. Whole lettuce plants were stored at optimal postharvest conditions (0 to 2 degrees C and 97% to 99% relative humidity). Measured parameters during each sampling day were relative water content (RWC), water content (WC), free water (FW), bound water (BW), free water to total water ratio (FW/TW), C, and OVQ. All parameters were evaluated in the external, middle, and internal zones of lettuce heads. The external zone had higher initial values of RWC, WC, and FW than the internal zone. The external zone yielded the highest FW/TW ratio (85%), indicating that external leaves had more water available to be used in degradation reactions and were more perishable, with the lowest shelf life if compared with the other lettuce zones. During storage, water status index evolution differed from zone to zone. An increase in BW and a decrease in FW were detected in all lettuce zones. RWC turned out to be a more sensitive measurement than WC. Yet RWC showed no significant correlation with any index. The OVQ parameter correlates with FW directly, or indirectly through FW/TW in all lettuce zones; therefore, FW is an objective and quantitative measurement, which impacts on the visual quality of butter lettuce. The decrease in chlorophyll content observed in the external leaves strongly correlated with the decrease in OVQ.

Dynamics of indigenous microbial populations of butter head lettuce grown in mulch and on bare soil.

The native microflora of lettuce cultivated in mulch and on bare soil and its evolution during storage at optimal condition were evaluated. Inner, mid, and outer leaves of the lettuce heads were analyzed separately and the evolution of the microbial populations were fitted to Gompertz and logistic models. The cultivation method (bare soil and mulch) introduced differences in the initial counts, evolution, and tolerance to refrigeration temperatures for some of the microbial populations under study. Most microbial populations from mulch lettuce presented a decline or little growth under refrigerated storage. However, populations from bare soil lettuce presented some growth phase during storage. Lactic acid bacteria from bare soil lettuce presented significant growth after 8 d of storage while LAB from mulch grown lettuce did not. Concurrently with the LAB growth, there was a decline in the coliform counts in bare soil grown lettuce. At the end of storage, the inner and mid leaves of mulch lettuce presented lower counts of psychrotrophic bacteria, LAB, and yeast and molds.