Post-harvest physico-mechanical properties of orange peel and fruit

Abstract

The post-harvest physico-mechanical properties data of fruits and vegetables are important in adoption and design of various handling, packaging, storage and transportation systems. Physico-mechanical properties namely, orange peel tensile strength and cutting energy and fruit color, weight loss, bioyield point, firmness, puncture force and cutting energy were determined with respect to storage period under ambient and refrigerated conditions. Peel tensile strength, modulus of elasticity and cutting energy decreased with storage period in both ambient and refrigerated conditions. The color index of orange followed a fourth-order polynomial equation during storage. At the end of 17 days storage, the fruit cumulative weight losses in ambient and refrigerated conditions were 19.4% and 7.3%, respectively. Bioyield point, firmness, puncture force and cutting energy of orange fruits decreased with respect to number of days of storage. The firmness of orange fruit was significantly higher in stem-calyx axis in vertical position than that in horizontal position.

Introduction

The mechanical harvesting of fruits causes damage from branches and other fruits as fruit falls from the tree and drops on the ground. These damages are in the form of splits, punctures and bruises. Further damage is caused when it is raked, picked up, loaded and transported to distant places by trucks. Generally, it takes several days in transportation from one place to another that causes various changes in physico-mechanical properties of fruits.

The post-harvest mechanical properties data of fruits and vegetables are important in adoption and design of various handling, packaging, storage and transportation systems. The fruit compression test simulates the condition of static loading that fruit can withstand in mechanical handling and storage. The most common practice to determine the fruit ripeness in field situation is pressing with ball of the thumb. Force deformation characteristics of fruits beyond the elastic limit may be important to simulate the destruction that occurs in bruising. Elastic modulus or Young’s modulus is often used by engineers as an index of product firmness. Puncture tests are also measures of firmness of fruits and vegetables to estimate harvest maturity or post-harvest evaluation of firmness.

Research has been carried out for several years to determine the resistance of fruits and vegetables to compression force. Witz (1954) reported resistance to bruising of potatoes to puncture by using a plunger. Studies on bruises to apples resulting from dropping and from application of pressure was reported by Gaston and Levin (1951).

Ahmed, Martin, and Fluck (1973) reported shear stress data of peel pieces collected at the time of harvest. Kaufmann (1970) measured the effect of water potential and temperature on the extensibility of citrus peel. Gyasi, Friedly, and Chen (1981) determined Poisson’s ratio for citrus fruit peel and pulp. Fidelibus, Teixeira, and Davies (2002) determined the gibberellic acid (GA₃) treatment effect on mechanical properties of pre-harvest orange peel and whole fruit. The properties such as color and firmness of orange that differentiate individual units of a product are important to determine the degree of acceptability of the product to the buyer (Guzel, Alizade, & Sinn, 1994). Fruit softening is often used as a criterion for estimating the feasibility of their storage or shelf life (Kader, 1992, Polderdijk et al., 1993, Blankenship et al., 1997).

Color is considered to be one of the most important external factors of fruit quality, as the appearance of the fruit greatly influences consumers. Fruit and vegetable yellowing is often a result of the disappearance of chlorophylls which allows the yellow orange xanthophylls and carotenes to become more visible (Shewfelt & Prussia, 1993). The relationship between color and level of maturation has been widely studied in tomatoes (Choi, Lee, Han, & Bun, 1995), peaches, and nectarines (Mitchell, 1987, Luchsinger and Walsh, 1993). Along the same line, Mercado-Silva, Benito-Bautista, and Garcia-Velasco (1998) identified L*, a*, and hue values as being the best parameters for differentiating the different stages of the maturation of guava. In citrus, Jimenez-Cuesta, Cuquerella, and Martinez-Javega (1981) proposed the use of the formula 1000a*/(L*b*) as “Color Index” for recording the process of orange degreening. In most fruits, their firmness diminishes as the degree of maturation increases due to the action of pectic enzymes during fruit maturation (Muramatsu, Kiyohide, & Tatsushi, 1996). Miller (1987) determined stress index, modulus of elasticity, and rupture force of freeze-damaged and non-damaged fruit. Sarig and Nahir (1973) reported the initial and permanent deformations of a creep test of citrus fruit to indicate firmness. Churchill, Sumner, and Whitney (1980) determined the influence of harvest date on the physical strength properties (burst and puncture) of whole fruit and tensile strength of peel pieces of three orange varieties. Singh (1971) studied optimum storage temperature, storage life and keeping quality of mandarins and sweet lemon. During storage the loss of moisture from the peel is continuously replenished by the movement of the moisture from the pulp. If this loss due to combined effect of respiration and transpiration goes on unchecked, the fruit shrivels up and becomes unmarketable.

There is a dearth of information on post-harvest physico-mechanical properties changes of orange peel and fruit under ambient and refrigerated storage conditions which are helpful to decide handling, packaging, storage, and transportation systems to be adopted and their designs. The objective of this paper is to report changes in basic physical and mechanical properties of orange peel and whole fruit under ambient and refrigerated fruit storage conditions.