Hydrothermal characteristics and quality of alfalfa cubes during transport
Khoshtaghaza, Mohammad Hadi
Alfalfa cubes are transported over long distances for export. The ambient conditions that the cubes may be exposed to in transit could vary from below freezing to in excess of 40°C and relative humidity up to 100%, especially when cubes are exported to humid regions of the Pacific Rim. Under humid condition, cubes absorb moisture and become prone to spoilage at high temperature. The objectives of this research were to determine time-temperature-humidity combinations for safe storage of cubes and to develop a model for estimating the hydrothermal dynamics of cubes during transport. Samples of commercial alfalfa cubes were exposed to combinations of temperatures from 9° to 39°C and relative humidities (RH) from 60% to 86% for 66 and 90 days in closed chambers. Cube moisture content, colour, density, hardness, durability, and time of appearance of molds were measured. Dynamic equations representing quality change with respect to time and storage conditions were developed. The cubes stored below 71% RH did not develop mold, but all of the cubes lost some degree of their greenness. Discoloration was severe at higher temperatures and humidities. Density, hardness, and durability of cubes declined significantly at 80% relative humidity. Data from instrumented containerized alfalfa cube shipments from Canada to Taiwan were analyzed. Temperatures and relative humidities were monitored during transit, and the moisture contents and durabilities of alfalfa cubes were measured on samples taken at the time of loading and unloading. The calculated spoilage potential agreed with the incidence of mold recorded at the time of unloading. Heat balance equations based on bulk thermal diffusivities and natural convection were developed. Several boundary conditions representing the dynamics of cube surroundings during shipments were investigated. It was shown that for prediction of the cube temperature, temperatures of both the head space above the cubes and the container ceiling were required. The moisture transfer within the cube pile in the container was modeled as a closed system, i.e., assuming no moisture transfer between inside and outside of the container. The calculated humidity ratio in the headspace was lower than the measured humidity ratio. It was concluded that the source of extra moisture inside the container was outside moisture penetrating into the container.