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Abstract
SUMMARY
Strawberry is highly perishable soft fruit, susceptible to mechanical injury, physiological deterioration, water loss and microbiological decay. Because of high susceptibility to attack by microorganisms and physical damage during handling, post-harvest life of strawberry (Fragaria x ananassa Duch.) is rather short, thus limiting commercial shelf life period of fruit. To reduce losses in crop, Postharvest decay and quality losses should be prevent to extend Postharvest period and maintain quality for export and domestic consumption. Therefore, the objectives of this study were to maintain quality and extending shelf-life of strawberry fruits. Strawberries were harvested with similar size at its ripe stage (80 % color stage as used for export). Damaged and non uniform Fruits were removed and good fruits were matched by color to remove unripe and overripe fruits. Fruits were subjected to different treatment. Control sample (fresh strawberry was packed in the high density polyethylene bags without any treatment. Each bag contain 250 gram about 25 strawberry fruit), water treatment (Wash).
Modified atmosphere packaging treatment, Lactic acid treatment and Lactic acid + modified atmosphere treatment. All these treatment were stored at 4°C. All samples untreated (control) and treated which sensorial accepted were subjected to microbiological,chemical and physical analyses during the storage time starting at day zero with interval of three days.
The study yielded the following conclusion:
1- Strawberry fruits which were used in this study ( festival cultivar ) contained 88.90 % Moisture, 5.11% total sugars 4.13% reducing sugars, 0.98% non reducing sugars, 7.2% total soluble solids, 0.64% total acidity ( as citric acid ) (3.57pH ) and 59.94 mg ascorbic acid /100 gm fresh weight basis.
2- Results of sensory evaluation revealed that colour, odour, texture and taste of control sample (untreated) were accepted up to day 6. For washed sample was accepted up to day 9. MAP samples were accepted up to day 12. LABS samples were remained acceptable up to day 15. While LABS+MAP sample was accepted up to day 19 of storage.
3- results of microbiological analysis showed that total psycrotrophic aerobic bacteria count for washed treatment after 6 days reached 4.9 log10 CFU/g while for MAP, LABS and LABS+MAP were 3.79, 2.85 and 2.44 log10 CFU/g respectively, the reduction obtained at day 6, for wash, MAP, LABS and lABS+MAP were 1.22, 2.33, 3.27 and 3.68 log10CFU/g respectively. At day 12 for MAP, LABS and LABS+MAP while washed sample was spoiled. Total psycrotrophic aerobic bacteria counts for MAP, LABS and LABS + MAP were 5.85, 4.57 and 3.42 log10 CFU/g respectively, after 15 days storage at 4°C, the number of total psycrotrophic aerobic bacteria count on strawberries treated with LABS + MAP was still similar to the initial number.
4- No growth of mold was detected for all treated samples, except for control and washed strawberries developed mold growth. (3.62 log10 CFU/g) after 6 days in control sample and 2.25 log10 CFU/g after 9 days of storage in washed sample.
5- The number of yeast in control sample at day zero was 2.1 log10 CFU/g this number was increased to 3.17 and 5.12 log10 CFU/g at day 3 and 6 respectively, while yeast number decreased to 1.47 log10CFU/g at day zero for wash sample and increased at day 3 and 6 but with a lower rate than control sample. At day zero and 3 for LABS treatment yeast was not detected but at day 6, yeast was 1.64 log10 CFU/g increased to 3.35 log10 CFU/g at day 15. This increasing did not affect the sensorial quality.
6- The result revealed that LABS treatment was more effective against yeast growth than MAP treatment but combined of LABS+MAP treatments showed the highest effect against yeast growth. Where there was no yeast growth detected at day zero, 3 and 6 in strawberries stored at 4°C and the shelf – life of this treatment was prolonged up to 19 day.
7- The limit for yeast is fixed at 105 CFU/g (5.0 log10 CFU/g), as microbiological criteria for minimally processed fruit by Debever (1996) because above this number spoilage of products due to yeast. growth become detectable for consumers (Fleet ,1992) .On the present work strawberries did not reached this limit during storage at 4°C up to day 15 in case of LABS treatment ( 3.35 log10 CFU/g ) and up to day 19 in case of LABS + MAB treatment (3.14 log10 CFU/g) (table 6). The LABS and CO2 in MAP had inhibiting effect on yeast growth.
8- Lactic acid bacteria number remained low about 2.84 to 4.78 log10 CFU/g at control samples at day Zero and days 6 and remained very low about 1.79 log10 CFU/g at day zero of treated strawberries with LABS to about 3.38 log10 CFU/g at day 12. The results revealed that Lactic acid bacteria confirmed these obtained for total psycrotrophic aerobic bacteria count.
9- Enterobactriaceae on day zero and day3 did not exceed the detection limit. Also for wash treatment Enterobactriaceae was not detected at day 0, 3 and 6 while for MAP, LABS and LABS+ MAP Enterobactriaceae was not detected up to 12, 15 and 19 day of storage respectively.
10.The combination of LABS + MAP combines the advantages of both systems (i.e. Inhibition of Enterobactriaceae, molds, yeast and prolongation of the sensory shelf-life).
11. It was clear that, by prolonging cold storage, moisture contents and total sugars content in all strawberry samples were decreased while reducing sugars contents were increased in the same time non reducing sugar contents in all strawberry treatments were decrease.
12. The results also showed that during cold storage, pH of all treated strawberries slightly decreased but total titratable acidity values of all strawberry treatments were slightly increased.
13. Results showed that strawberry samples which treated with LABS +MAP had the highest T.S.S content followed by strawberries which treated with MAP, LABS, wash and control sample had the lowest T.S.S content.
14. The obtained results indicated that fresh strawberry fruits (at a zero time) contained 59.94 mg/100g ascorbic acid. Ascorbic acid contents of strawberry samples washed with water were lower than of all other treated samples. While LABS+MAP sample was the highest ascorbic acid content at all days of storage time.
15. The results indicated also that Strawberry sample which treated with LABS+MAP had the lowest weight loss percentage followed by MAP, wash sample and LABS.