Development of a texture evaluation system for winter jujube (Ziziphus jujuba ‘Dongzao’)

Winter jujube (Ziziphus jujuba 'Dongzao') is an excellent late maturing variety of fresh-eating jujube in China. Fruit texture is an important indicator of sensory quality. To investigate the correlations among texture indices and establish an evaluation system for winter jujube texture, we used the TMS-Touch instrument to perform a texture profile analysis (TPA) on 1 150 winter jujubes from three major producing areas in China. Eight indices and their best-fit distribution were obtained, including fracture (Pearson), hardness (InvGauss), adhesive force (Weibull), adhesiveness (LogLogistic), cohesiveness (LogLogistic), springiness (BetaGeneral), gumminess (InvGauss), and chewiness (InvGauss). Based on the best-fit distribution curves, each index was divided into five grades (lower, low, medium, high and higher) by the 10th, 30th, 70th and 90th percentiles. Among the texture indices, 82% of the correlation coefficients were highly significant (P<0.01); meanwhile, chewiness was significantly (P<0.01) and positively correlated with springiness and gumminess, of which the correlation coefficients were up to 0.8692 and 0.8096, respectively. However, adhesiveness was significantly (P<0.01) and negatively related to adhesive force with a correlation coefficient of –0.7569. Among hardness, cohesiveness, springiness, gumminess, and chewiness, each index could be well fitted by a multiple linear regression with the remaining four indices, with the coefficients above 0.94 and the mean fitting error and mean prediction error lower than 10%. A comprehensive evaluation model was consequently established based on factor analysis to evaluate the texture quality of winter jujube. The results demonstrated that winter jujube with higher comprehensive scores generally exhibited higher springiness and chewiness, but had lower adhesive force and adhesiveness. We used factor analysis and clustering analysis to divide the eight studied texture into four groups (cohesive factor, adhesive-soft factor, tough-hard factor, and crispness factor), whose representative indices were springiness, adhesiveness, hardness, and fracture, respectively. Overall, this study investigated the variation in each index of winter jujube texture, explored the association among these indices, screened the representative indices, and established a texture evaluation system. The results provide a methodological basis and technical support for evaluating winter jujube texture.