Active packaging and new preservation methods for extending shelf life of fresh strawberries

The objective of this research was to investigate the effect of active packaging and new preservation methods for extending shelf life of fresh strawberries. Gas composition inside the package, pH, total soluble solids, electrical conductivity, color, texture profile, decay incidence and FT-NIR analyses were performed to investigate the effect of treatments on the quality criteria of strawberry during 4 weeks storage at +40C. This Ph. D. dissertation work is divided into six parts.In the first part, effectiveness of two types of oxygen absorbers (ATCO-100 and ATCO-210) on quality of fresh strawberries is reported. Loss of total soluble solid content, color properties and texture characteristics were higher in the control groups compared with the ATCO-100 and ATCO-210 absorbers. There were no significant differences in total soluble content, pH value, electrical conductivity, color values, textural parameters and decay incidence among the ATCO-100 and ATCO-210 groups, but difference between treatment groups and control is statistically significant. ATCO-100 and ATCO-210 had significant effect on extending shelf life of strawberry.In the second part, the effect of different scavenging systems (carbon dioxide and oxygen) on quality of fresh strawberry was studied. Strawberry was treated with one oxygen scavenger (ATCO-210) and two different carbon dioxide (EMCO-A and EMCO-B) scavengers throughout storage. The package headspace with EMCO-A and EMCO-B absorbers, exhibited the lowest CO2 accumulation compared with ATCO and control. EMCO-B had significant effects on brix and electrical conductivity of strawberry during storage. No significant color differences were found among EMCO-A, EMCO-B and ATCO treatments. Results of sensory evaluation showed that, EMCO-B and ATCO had the highest desirable scores for general acceptability. Firmness values of control group were significantly lower than that of the EMCO-A, EMCO-B and ATCO groups.In the third part, the efficiency of various concentrations (3, 6 and 9 ppm) of ClO2 was evaluated. All treatments (3, 6 and 9 ppm) were effective in retaining pH, brix, electrical conductivity and textural parameters compared with control. 3 ppm ClO2 had no significant effect in preventing a value (redness) change of strawberry. 6 ppm ClO2 was the best treatments to delay consumption of oxygen and maintain the titratable acidity of strawberry.In the fourth part, various ultrasound powers (30W, 60W, 90W) and exposure times (5 and 10 min) were used to maintain quality of strawberry. 30W and 60W ultrasound treatments were effective for eliminating quality deterioration of fresh strawberry compared with control and 90W treatment. No significant effects were found for exposure time within treatments. 90W treatments damaged the strawberry tissue and shorten the shelf life. 30W and 60W treatments maintained the pH, total soluble solid, electrical conductivity, color and texture parameters of strawberry than the untreated control and 90W treatment. Mold decay was the highest for control group.In the fifth part, different ozone concentrations (0,075ppm, 0,15 ppm, 0,25 ppm) and exposure times (2 and 5 min) were applied to strawberry. Results showed that 0,075 ppm and 0,15 ppm treatments significantly maintained the quality of strawberry. There were not any significant differences associated with exposure times. 0,075 ppm and 0,15 ppm treatments were effective to delay changes in pH, total soluble solid, electrical conductivity and texture parameters which were related with shelf life. All treatments had bleaching effect on strawberry. 0,075 ppm had the lowest and 0,25 ppm had the highest undesirable color changes among the treatments. High concentration of ozone had a negative effect on quality of strawberry.In the last part; the best results found on third (6 ppm ClO2), fourth (30 W) and fifth (0,075 ppm O3) studies were selected to compare the effects on strawberry quality. Also effectiveness of combined effects of 6 ppm ClO2+30W and 0,075 ppm O3+30W were investigated on quality criteria of strawberry. Results demonstrated that, combined effect of 6 ppm ClO2+30W and 0,075 ppm O3+30W had positive effect on reducing respiration rate, inhibiting the mould decay and delayed changes in pH, brix, electrical conductivity, color and textural properties. Individual treatments (6 ppm ClO2, 30W and 0,075 ppm O3) were also effective to maintain quality of strawberry compared to control group.Furthermore, FT-NIR spectra?s which were gotten by all parts of this study, gave comprehensive information about the strawberry during storage and showed the high potential of FT-NIR spectroscopy as a rapid, economical and nondestructive measurement technique.