Effect of Mineral Packing Films on Preservation of Fresh Fruits

Abstract

The necessity of a functional packing material to prevent fresh fruits from decaying has been increased. The polyethylene (PE) film is one of the most common packing materials. It has a number of advantages such as low cost, ease to manufacture with many different forms, transparency and light weight. However, it is hard to preserve the fresh food in a PE film for a long time because the PE film is a poor barrier to oxygen and water vapor transmission compared to glass or metal. The functional packing materials including mineral powder (loess, barley stone, jade, zeolite, charcoal, kaolin, feldspar, biotite and selenium) were manufactured to overcome the problems of PE film. Pulverization of mineral powder was important to form the mineral film. Thus, self-grinding method was used for pulverization of mineral powder in this study. The optimum feeding conditions for grinding of mineral powder were found 0.45 kg/h and 0.91 kg/h inputs of mineral material. Also, due to the beige color of the mineral powder, the mineral film leads to reduce transparency. The opacity of the packing film could be a limitation for a consumer use. Hydroxyl apatite was used to improve the opacity. The hydroxyl apatite 0.5 wt% and mineral powder 2.5 wt% (HAP-3) was effective for improvement of opacity of the film. The transmission rates of relative humidity and oxygen of the mineral packing film were 5.4 g/(m2∙24 h) and 2100 cm3/(m2∙24 h∙atm), respectively. They were decreased by 26.0% and 41.7% compared with PE packing film. The tensile strength of the mineral packing film was 1.25 fold higher than that of PE packing film. To determine the effect of the mineral film on storability of fresh fruits, persimmon, tomato and banana were selected as samples. Compared to PE packing film, the mineral packing film should better behaviors on color index, firmness retention and total soluble solids of persimmon and tomato. Consequently, mineral-packing material was able to maintain the sensory and physicochemical qualities of fruits at a higher level compared with PE packing film. It could be explained as its lower relative humidity transmission rate. As the result of a lower relative humidity transmission rate, the mineral film offered a larger resistance to water vapor and gas transmission during the entire storage time. However, peel spotting and pulp to peel ratio of banana showed very little difference between mineral film and PE film. There was a difference of the effect on maintaining quality of fruits among the climacteric fruits. According to related researches, banana has higher respiration rate and ethylene production than other fruits. The manufactured mineral film had a negative impact on the quality of banana. As the results, the fruit with high respiration rate and ethylene production such as banana had a bad effect on the quality of fruits. Therefore the mineral film may appropriate to the fruits with normal respiration rate and ethylene production such as persimmon and tomato. More research will be needed to investigate the certain mechanism that mineral film functions during storage to facilitate the application of packaging technology in a broader range in the future.