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Abstract
SUMMARY
Vegetables are useful crops which are very important for daily consumption in developing and developed countries because they are cheap and constitute a food source of carbohydrates, vitamins, fibers, like leafy vegetables in particular are a rich source of antioxidants such as beta-carotene and ascorbic acid.
An increasing demand was observed on minimally processed vegetables called ready-to-use. People prefer healthy foods but have little time for food preparation. This trend also indicates a preference for vegetables that is easy to prepare, convenient to eat at work and while traveling.
The marketing of minimally processed fruits and vegetables is limited by a short shelf life and rapid deterioration of their components due to tissue damage as a result of processing. Therefore, the aim of this investigation was to prolong the shelf life of minimally processed vegetables, maintain their fresh appearance and stop or delay microbial growth. In this study five crops of vegetables: Carrot, Green beans, Summer squash, Okra and Jew’s mallow, were taken according to daily consumption in Egyptian society.
Fresh vegetables were brought, sorted, grated, washed with tap water, peeled, cut or shredded, undesirable parts were removed, dipped into different concentrations of disinfection solutions -chlorine or lactic acid -, removed, dried, packaged in low density polyethylene bags, and stored in a refrigerator at 5±1˚C. Sensory evaluation was determined by panelists. Microbiological analysis was carried out by counting of psychotrophic bacteria, yeast, mold and Enterobacteriaceae group. Chemical properties including moisture content, pH value, total titratable acidity, and total soluble solids were also determined. Finally, the obtained data were statistically analyzed. The obtained results of the present study could be summarized in the following points:
1. The results of sensory evaluation of minimally processed vegetables revealed that the sensory score of samples treated with different concentrations of chlorine or lactic acid had the same value for color, odor, texture and overall acceptability as control samples (5.00). These results concluded that disinfection solutions with different concentrations used didn’t affect the quality attributes of vegetables.
2. Results also indicated that carrot was accepted according to quality attributes up to 15 days only for untreated samples, while samples treated with 50, 100 and 150 ppm chlorine were accepted up to 15, 20 and 25 days respectively while samples treated with 1, 1.5 and 2% lactic acid were accepted for 20, 15 and 10 days respectively.
3. The obtained data of sensory evaluation revealed that green beans was accepted up to 10 days only for control samples. Samples treated with 50, 100 and 150 ppm chlorine were accepted up to 15, 20 and 25 days respectively, while samples treated with 1, 1.5 and 2% lactic acid were accepted for 20, 15 and 10 days respectively.
4. results of sensory evaluation obtained for Summer squash treated with 1, 1.5 and 2% lactic acid were accepted for 25, 15 and 10 days respectively while samples treated with 50, 100 and 150 ppm chlorine were accepted up to 15, 15 and 20 days respectively. in contrast control was spoiled after day 10.
5. It was clear that minimally processed Okra treated with1% lactic acid still accepted with fresh appearance up to day 17 under cold storage while Okra treated with 100 ppm chlorine was accepted up to day13, the shelf life of Okra treated with 0.5% lactic acid or 50 ppm chlorine was accepted up to day 9, in contrast control was spoiled after day 6.
6. Results indicated that minimally processed Jew’s mallow treated with 100 ppm chlorine was accepted with fresh appearance up to day 13 days during cold storage. Also it was found that Jew’s mallow treated with 0.5 % lactic acid or 50 ppm chlorine were accepted up to day 9, control with 1% lactic acid was spoiled at day 6.
7. Results emphasized that moisture percentage of all minimally processed vegetables treated with different concentrations of chlorine or lactic acid didn’t affected and was almost constant during the shelf life.
8. Chemical analysis showed that pH value of carrot slightly increased during the shelf life in all treatments, it was 6.93 at zero day and reached 7.59 at day 25 for 150 ppm chlorine treatment which was the most effective one. For green beans, pH value was 6.40 at zero day and reached 7.88 at day 25 for the effective one (150 ppm chlorine). pH value of summer squash and okra slightly increased during the shelf life. Summer squash and okra treated with 1% lactic acid had the longest shelf life with pH values of 6.85 and 6.26 at zero day and reached 8.00 and 7.98 after 25 and 17 days respectively. Also, pH value of minimally processed Jew’s mallow treated with 100 ppm chlorine was 7.24 at zero day and reached 8.25 after 13days of storage.
9. Data indicated that titratable acidity decreased during the storage in all treatments but control showed more decrement during storage. Titratable acidity of carrot slightly decreased during the shelf life in all treatments, it was 0.31 at zero day and reached 0.14 at day 25 for 150 ppm chlorine. In green beans, the same result was found whereas titratable acidity was 0.22 at zero day and reached 0.12 at day 25 for 150 ppm chlorine treatment. Titratable acidity of summer squash and okra slightly decreased during the shelf life in all treatments and control. Summer squash and okra treated with 1% lactic acid had the longest shelf life with titratable acidity of 0.44 and 0.24 at zero day and reached 0.20 and 0.14 after 25 and 17 days respectively. Titratable acidity of minimally processed Jew’s mallow treated with 100 ppm chlorine was 0.16 at zero day and reached 0.10 after 13days of storage.
10. Results revealed that TSS slightly increased in all treated and untreated minimally processed vegetables but didn’t affect the quality, with slight differences among samples.
The data of microbiological analysis indicated that using 150 ppm chlorine reduced the total psychotrophic counts of minimally processed carrot and green beans by 1.37 and 1.19 log cfu/g units respectively at day zero; it had the highest inhibition effect on total psychotrophic count during the shelf life of carrot and green beans. Also it was concluded that using 1% lactic acid reduced the total psychotrophic counts of minimally processed summer squash and okra by 1.45 and 1.17 log cfu/g units respectively at day zero, it was the most effective on total psychotrophic