Abstract:
Sweet cherry (Prunus avium L.), an economically important nutritious fruit, is popular for its attractive red colour and high antioxidant potential. Most sweet cherries are consumed fresh and a small proportion of the total sweet cherry production is valuable to make processed food products. Sweet cherry is a highly perishable product due to its high respiration rate and rapid softening process at room temperature (approximately 20 ℃), which ultimately causes the color changes, weight loss, browning and changes of nutrients and restricts its shelf life. The objective of this study was to establish a comprehensive evaluation method for the fruit quality of sweet cherry using factor analysis, and to clarify the relations among the indices in order to select sweet cherry varieties with good quality. There were 11 quality indicators for 24 sweet cherry cultivars evaluated on the base of principal component analysis and fuzzy evaluation, including single fruit weight, hardness, edible rate, juice yield, pH value, total sugar content, reducing sugar content, titratable acid content, sugar acid ratio, vitamin C content and anthocyanin content. Principal component analysis is a mathematical tool which performs a reduction in data dimensionality and allows the visualisation of underlying structure in experimental data and relationships between data and samples. The result showed that different quality indicators and sensory evaluation among tested sweet cherries were different. There were significant correlations between single fruit weight and vitamin C, between edible rate and juice yield, titratable acid, between anthocyanin and pH value, titratable acid, and between total sugar, reducing sugar, sugar acid ratio and pH value. Five main factors were extracted by factor analysis, which included sweet taste, flavor, antioxidation, edible rate and quality, and the cumulative contribution approached to 82.948%. Total sugar, juice yield, vitamin C content, edible rate and single fruit weight were selected as key indicators to evaluate sweet cherry qualities. The scatter plot of the 5 factors showed the distribution of fruit cultivars by PAST software. The comprehensive scores of the varieties were ranked. The top 10 cherry varieties were ranked as Red (0.70), Zaolu (0.63), Red honey (0.60), Colored jade (0.47), Qinying-1 (0.44), S2S1 (0.38), Early fruit (0.35), 13-33 (0.28), Bright pearl (0.13), and Qinlin (0.07). The fuzzy comprehensive evaluation of 11 analysis indicators showed that the top 10 varieties of comprehensive quality performance were Red (0.642), Red honey (0.566), Zaolu (0.545), Bright pearl (0.524), Colored jade (0.521), Qinying-1 (0.512), Qinlin (0.501), Early morning (0.491), S2S1 (0.482), and Early fruit (0.470). The score was ordered by comprehensive score and the 8 analytical indices were analyzed by fuzzy evaluation. Consistent results were obtained that the cultivars of Red, Zaolu, Red honey, Color jade, Qinying-1, S2S1, Early fruit, Bright pearl, and Qinlin were selected as the suitable sweet cherries. The cultivar Red has the highest comprehensive quality, and it can be utilized as the raw material for the breeding, refining, developing and utilization of prunus species. The result of factor analysis was consistent with that of PCA score plots. These results determined the top 9 cherry varieties for use as a breeding stock for future cherry variety development.