Beyond Fresh-Cut: Addressing Critical Aspects for Fresh Strawberry Puree

The present study was aimed to address critical aspects related to the development of fresh-blended strawberry purees. The main focus was to evaluate and determine the effects of wounding intensity on respiration rate and biologically active compounds (Experiment 2.1), to survey most important strawberry cultivars grown in Italy for fresh-blended purees (Experiment 2.2), optimize the blending conditions (time and temperatures) (Experiment 2.3), and evaluate and compare packaging conditions using two different plastic materials under active and passive modified atmosphere conditions (Experiment 2.4). For this purpose, fresh purees were blended and samples were prepared and physiochemical, nutritional and sensorial attributes were monitored at initial and during storage at 5°C (according to each experiment). In Experiment 2.1, fruits were submitted to six levels of cut intensity - whole fruit (WHO), 4, 16, 64, and 128 pieces and chopped (CHO) samples. Respiration rate, vitamin C, total phenolic content, antioxidant capacity, total anthocyanin content, total soluble solids, titratable acidity and pH values were evaluated at the processing day (Day 0) and after 2 days at 5 °C (Day 2). Results showed effects of increased respiration rate consequential from cell disintegration of wounded issue up to certain wounding degree (64 pieces cutting), could be minimized significantly at a higher wounding intensity (cutting into 128 pieces and chopped) in strawberry fruits. This resulted in significant increase in total phenolic content, dehydroascorbic acid, antioxidant capacity during storage time with no effects on total anthocyanin content, total phenolic content, pH value and sugar/acid ration content. These results should be considered for processing and packaging optimization of minimally processed strawberries. For experiment 2.2, fresh puree from six strawberry cultivars (‘San Andreas’, ‘Sabrina’, ‘Candonga’, ‘Festival’, ‘Fortuna’ and ‘Nabila’) were evaluated upon blending. Despite the variability on nutritional attributes, no significant difference on vitamin C content and sensory attributes except sensory color among the studied cultivars was found. Inverse correlation (r=76) (P<0.001) of total color difference (ΔE*) and total anthocyanin content, and positive correlation (r=0.80; P<0.001) of total phenolic content and antioxidant capacity were found. ‘Festival’ followed by ‘San Andreas’ and ‘Candonga’ were mentioned as suitable cultivars for fresh strawberry puree production under optimal blending conditions. Therefore, to optimize the effects of blending conditions (time and temperature) on quality attributes of fresh-blended strawberry puree, two independent trails - response surface method based on a central composite design (Trial I) and blending temperature (Trial II) were conducted. For Trial I, ten different blending time/temperature experimental runs ranging from 5 to 140 s and from 0 to 21°C respectively were tested. Physicochemical, organoleptic and nutritional quality attributes were evaluated as responses at the processing day (Day 0) and after 6 days at 5°C (Day 6). All data were fitted to the second-order (quadratic) regression equation. Results showed that at day 0, blending time had significantly negative effect on L* and b* values, titratable acidity and succinic acid, whereas blending temperature had significant influences on total anthocyanin content, sucrose, fructose, and malic acid. After 6 days, however, viscosity, total anthocyanin content, and dehydroascorbic acid were the only parameters found to be significantly affected by the blending conditions. High blending temperature (21°C) had positive effect on total anthocyanin content and negative effect on dehydroascorbic acid content. Therefore, Trial II was aimed to better understand the effect of this factor on certain quality parameters during storage of fresh purees. Strawberries stored at 5 or 21°C overnight were blended at 4000 rpm for 90 and stored for 13 days at 5°C. Color parameters vitamin C, total anthocyanin content and sensorial attributes were monitored after 0, 3, 8 and 13 days at 5°C. A two-way analysis of variance and Tukey’s test (P<0.05) showed that after 3 days, samples blended at the lowest temperature showed significantly better color maintenance (lower ΔE*), aroma and overall acceptance and stable ascorbic acid content. In general, blending time less than 90 s and temperature 5 °C can be optimal blending conditions with improved packaging conditions. Finally, Experiment 2.4, was aimed to evaluate and compare two packaging materials, namely polypropylene/ethylene vinyl alcohol (PP/EVOH) and polypropylene/polyamine (PP/PA), both under active (5% O2+13% CO2) and passive (air) modified atmosphere packaging (MAP), to package fresh-blended strawberry purees. Physicochemical, sensorial, nutritional attributes and spoilage microbial counts were evaluated after 0, 2, 6, and 12 days of storage at 5°C. A two-way analysis of variance for treatment, storage time and their interactions was run and significant means were separated by Tukey’s test (P<0.05). Results showed that after 12 days at 5°C, packaging significantly affected the physical and nutritional attributes and microbiological counts. Samples in active MAP in PP/EVOH or PP/PA maintained slightly higher nutritional and sensorial attributes during storage. After 12 days at 5°C, samples in active PP/EVOH had lower microbiological counts (< Log 4 CFU g-1) and no perceived off-flavor compared to the other treatments. In conclusion, fresh-blended strawberry purees can be stored for about 12 days at 5°C using active PP/EVOH MAP condition for quality maintenance and freshness. As a final remark, high convenience fresh-blended strawberry puree can successfully be developed without significant losses of nutritional, organoleptic attributes for ready-to-use with 100% fruit product puree. The influences of pre-harvest factors on quality and flavor profiles and non-thermal processing techniques should be considered for future studies.