Improving Shelf Life, Quality, and Safety of Locally Grown Vegetables in Kansas

Limited access to refrigerated facilities, as well as gaps in knowledge regarding postharvest handling and food safety, are significant barriers for local growers to increase vegetable production. Data collected at the 2015 Great Plains Growers Conference indicate that only 32% have access to quick cooling facilities, and 6% to refrigerated trucks. The aim of this project was to investigate the effect of modified atmosphere packaging (MAP) and postharvest washing with ozonated water on the shelf life of locally–grown vegetables. Local organic spinach were divided into six treatments: unwashed stored in open produce bag (OPB) (CC) and stored in MAP bags (CM); washed in cold water (4 °C) and stored in OPB (WC) and stored in MAP bags (WM), washed in ozonated water stored in OPB (OC) and in MAP bags (OM). All groups were stored at 13 °C/85% RH until the end of storage. Daily CO₂ and O₂ concentrations inside the MAP bags were measured. Subjective and objective quality was evaluated on the day of harvest and every three days during storage. Numerical rating scales for overall quality, and off odors were used to evaluate the groups. Additionally, 50 leaves from each group were individually rated for subjective analysis of visual quality, decay, color, texture, and wilting. Color (CIE L*a*b*) and texture (compression shear-test with 5-blade probe) was also evaluated. Microbiological analyses were conducted to enumerate psychrotroph, total aerobic microorganism (APC), generic Escherichia coli, coliform, yeast and mold populations (Y&M). Internal atmosphere reached equilibrium in three days, and ranged from CM 6.8-8.26% CO₂ and 5.40-7.47% O₂, WM 6.11-6.56% CO₂ and 6.34-10.70% O_2, and OM 7.04-7.47% and 2.68-9.75% O_2. The CC was brighter (higher L* of 47.35 compared to 41.12-43.07 of other groups), less green with OC (lower a* of -13.86 and -13.33, respectively, compared with -15.83- -16.67) and more yellow (higher b* of 36.82 compared to 28.54-30.57). The most effective treatments were the combination of washing procedures (independent of water type) with MAP (WM and OM), both of which lasted for 18 days in comparison to 6–9 days for CC.  Escherichia coli and coliform populations were < 1.0 Log₁₀ CFU/g throughout storage for all treatments. In general, psychrotroph, APC and Y&M populations steadily increased throughout storage, regardless of treatment.  Thus, the treatments appeared to have a greater impact on quality than microbial populations. Further experiments with other crops (broccoli, asparagus, and beets) will be conducted to validate these results.