Passion Fruit Ripening Stages Divided by Logistic Growth Model with Multiple Quantifiable Indicators

  Objective  To effectively determine the summer growth and development as well as the fruit formation and maturation of passion fruit applying logistic model was studied.

  Method  Physiochemical parameters including transverse and longitudinal diameters, solid to acid ratio, pulp percentage, pericarp thickness, and firmness of Qinmi No. 9 passion fruit were monitored as the plant grew and fruit developed. A logistic growth model incorporating those quantifiable indicators was evaluated to classify the fruit maturity stages by a factor analysis.

  Result   In terms of longitudinal and transverse diameters, the passion fruit grew in a slow-fast-slow pattern. Once the effective accumulated temperature in growth degree days (GDD) reached 440 ℃·d, the fruit essentially had completed the enlargement stage. Thereafter, the solid to acid ratio and pulp yield of the fruit were in an S-shape trend, while the peel thickness and fruit firmness in a declining cubic function. A significant correlation was observed between the indicators and GDD. With the factor analysis-generated assessment index, I_M, the mathematic model built with the logistic growth function showed a high fitting of 99.25% on fruit maturity. Three growth transition points, t₁, t₂, and t₃, distinctively separated the fruit development into (A) the pulp weight gaining stage with a GDD of 475–736 ℃·d, (B) the color-changing stage with a GDD of 736–997 ℃·d, and (C) the ripening stage with a GDD of 997–1200℃·d.

  Conclusion  The analysis based on the selected quantitative physiochemical indicators effectively divided the maturation of Qinmi No. 9 passion fruit into the pulp weight gaining, color-changing, and ripening stages. The result would facilitate the design of automated fruit picking and storage management.