María Victoria Agüero

Assessment of lettuce quality during storage at low relative humidity using Global Stability Index methodology

Abstract During postharvest, lettuce is usually exposed to adverse conditions (e.g. low relative humidity) that reduce the vegetable quality. In order to evaluate its shelf life, a great number of quality attributes must be analyzed, which requires careful experimental design, and it is time consuming. In this study, the modified Global Stability Index method was applied to estimate the quality of butter lettuce at low relative humidity during storage discriminating three lettuce zones (internal, middle, and external). The results indicated that the most relevant attributes were: the external zone - relative water content, water content , ascorbic acid, and total mesophilic counts; middle zone - relative water content , water content, total chlorophyll , and ascorbic acid; internal zone - relative water content, bound water, water content, and total mesophilic counts. A mathematical model that takes into account the Global Stability Index and overall visual quality for each lettuce zone was proposed. Moreover, the Weibull distribution was applied to estimate the maximum vegetable storage time which was 5, 4, and 3 days for the internal, middle, and external zone, respectively. When analyzing the effect of storage time for each lettuce zone, all the indices evaluated in the external zone of lettuce presented significant differences (p < 0.05). For both, internal and middle zones, the attributes presented significant differences (p < 0.05), except for water content and total chlorophyll.

Delayed Cooling or Suboptimal Storage Temperatures Reduce Butterhead Lettuce Shelf-Life

Crated or uncrated butterhead lettuce (Lactuca sativa L.) var. Lores responds to environmental conditions during early postharvest, the first 24 h after harvest. The present work examines the effects of environmental conditions during early postharvest on quality indices in refrigerated storage. Additionally, effects on shelf-life were estimated using the modified Global Stability Index methodology. Quality indices at the start of storage were higher for heads exposed to optimal conditions immediately after harvest than for heads exposed to suboptimal ones. Despite these initial differences, changes in almost all quality indices were independent of storage condition. Similar responses were found for water content, bound and free water, ascorbic acid, total chlorophyll, and overall visual quality. Changes in relative water content and mesophilic bacteria counts during refrigerated storage were a function of environmental condition during the first 24 h after harvest. Maintenance of optimal environmental conditions during the first hours after harvest prolonged shelf-life to 12 days compared to heads exposed to suboptimal conditions during the early postharvest period. These results impact marketing of the produce and support the idea that proper handling during early postharvest diminishes quality loss and prolongs shelf-life, allowing butterhead lettuce to reach more distant markets.

Early Postharvest Time Period Affects Quality of Butterhead Lettuce Packed in Crates

The period between when butterhead lettuce (Lactuca sativa var. L) heads are harvested and stored in cold rooms can be up to 24 h. During this period, environmental conditions are uncontrolled, and heads could undergo deterioration that has not been previously quantified. Quality changes of lettuce heads packed in crates and exposed to optimal or suboptimal conditions during the 24 h after harvest were evaluated. The effect of placement within crates (lower, middle, and upper layer) was assessed. Proximity of heads within crates created a barrier to transfer of heat and humidity. This resulted in negative responses for plants under optimal conditions because there was a delay in temperature reduction and a deterioration in quality. At suboptimal conditions the response was positive because respiration and transpiration allowed development of a saturated environment around heads, delaying loss of quality. This effect was most obvious in heads from middle and lower layers, which presented the highest overall visual quality and water content. Use of crates caused extensive mechanical damage on heads, making it necessary to discard outer leaves, leading to 10 and 35% weight losses under optimal and suboptimal conditions, respectively. Initial quality rapidly decreases in the first day after harvest. It is necessary for technologies to be upgraded to reduce quality and economic losses.

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 brewers 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.

Evolution of quality indices of fresh bunched spinach stored using low density polyethylene and polypropylene bags

Packaging technology constitutes an available method for reducing postharvest deteriorative processes on fresh products. The purpose of this work was to evaluate leaf water status, weight loss and colour retention of bunched spinach leaves packaged in low density polyethylene (LDPE) and polypropylene (OPP) bags, stored at 2°C for 25 days. Water status was determined through relative water content (RWC), the free:total water ratio (FW/TW) and bound water (BW); colour was evaluated colorimetrically as hue angle. Gaseous concentrations reached in OPP bags (11% O 2 , 3%–5% CO 2 ) were within those considered beneficial for spinach. Weight loss was higher in LDPE than OPP bags. RWC was lower in LDPE than in OPP bags. RWC decreased after day 18. Increases occurred in BW and decreases occurred in the FW/TW, indicating possible water movement within the leaf. Hue angle diminished after seven days of storage, indicating loss of green colour. Better physical and physiological properties were observed in spinach packaged in OPP bags.