Maturity sorting index of dragon fruit: Hylocereus polyrhizus

The purpose of this research was to investigate maturity prediction of red flesh dragon fruit based on non-destructive measures. Specific weight, sphericity, color value L, a, b and light reflectance spectrum were linearly combined by partial least squares regression (PLSR) analysis. The PLSR models could predict days after fruit set, weight ratio and total soluble solids relatively well with standard deviation divided by standard error of prediction (RPD) of 2.86, 2.45 and 2.38, respectively. Date after fruit set, total soluble solids, total acid, ratio of total soluble solids and total acidity and weight ratio were transformed into a principal component 1 (PC1) by the principal component analysis and used to represent a single maturity index. The PLSR model with non-destructive parameters resulted in an improved performance in the prediction of the maturity index (PC1) with a RPD increase to 3.49. The model could be further simplified but retained a comparable accuracy by the application of a log (R680/R550) in place of the light reflectance spectrum.     

Effects of pressurized carbon dioxide on controlling Sitophilus zeamais (Coleoptera: Curculionidae) and the quality of milled rice

Carbon dioxide was applied at atmospheric pressure (1 bar) and under higher pressures (4, 6 and 8 bars) using a specially designed pressure chamber with the intention of killing Sitophilus zeamais in milled rice. Pressures of 4, 6 and 8 bars shortened the exposure time required to obtain 99% mortality of all life stages of S. zeamais from 148 h at atmospheric pressure to 29, 9.0 and 4.8 h respectively. Adults were the most susceptible stage in all the treatments. Pupae were the most tolerant stage at atmospheric and low pressure (4 bars) but at higher pressure (6 and 8 bars) no difference among immature stages was found. After application of carbon dioxide under pressure, a significant decreasing trend (P < 0.05) was observed in water absorption, cooked rice hardness, final viscosity, setback and consistency with prolonged exposure time. High pressure produced more distinctive changes than low pressure. However, panelists could not detect any differences between non-treated and treated rice when sensory qualities were evaluated.     

Non-destructive maturity classification of mango based on physical, mechanical and optical properties

Mango is a popular tropical fruit and right maturity at harvest is important for eating quality and shelf life. Therefore, harvesting needs skilled pickers otherwise fruit of varying levels of maturity will be collected. This research investigated maturity classification of mango fruits (cv. Nam Dokmai) using physical, mechanical and optical properties. Variation in size, sphericity, specific gravity, total soluble solids, total acidity, surface color, acoustic response (stiffness coefficient based on the resonant frequency and the weight of the fruit), impact response (peak acceleration/corresponding time) were followed during a number of days after fruit set from 77 to 115 days. On discriminant analysis, mangoes of three maturity classes based on days after fruit set could be separated using non-destructive parameters (95%). Cluster analysis was applied based on destructive parameters (total soluble solids and total acidity) and days after fruit set to pre-allocate each fruit into four different maturity classes. The 89.0% accuracy of classification into four levels of maturity could be achieved by simplified non-destructive model. The best applicable variables of physical, mechanical and optical properties were SG, stiffness coefficient and diffuse reflectance at 670 nm, respectively.