Efficient preservation of sprouting vegetables under simulated microgravity conditions

Abstract

The effectiveness of a simulated microgravity environment as a novel method for preserving the freshness of vegetables was investigated. Three types of vegetables were selected: vegetable soybean, mung bean sprouts, and white radish sprouts. These selected vegetables were fixed on a three-dimensional rotary gravity controller, rotated slowly. The selected vegetables were stored at 25°C and 66% of relative humidity for 9, 6, or 5 d while undergoing this process. The simulated microgravity was controlled utilizing a gravity controller around 0 m s-2. The mung bean sprouts stored for 6 d under simulated microgravity conditions maintained higher thickness levels than the vegetable samples stored under normal gravity conditions (9.8 m s-2) for the same duration. The mass of all three items decreased with time without regard to the gravity environment, though the samples stored within the simulated microgravity environment displayed significant mass retention on and after 3 d for mung bean sprout samples and 1 d for white radish sprout samples. In contrast, the mass retention effect was not observed in the vegetable soybean samples. Hence, it was confirmed that the mass retention effect of microgravity was limited to sprout vegetables. As a result of analysis harnessing a mathematical model, assuming that the majority of the mass loss is due to moisture loss, a significant difference in mass reduction coefficient occurs among mung bean sprouts and white radish sprouts due to the microgravity environment, and the mass retention effect of simulated microgravity is quantitatively evaluated utilizing mathematical models. Simulated microgravity, which varies significantly from conventional refrigeration, ethylene control, and modified atmosphere, was demonstrated effective as a novel method for preserving and maintaining the freshness of sprout vegetables. This founding will support long-term space flight missions by prolonging shelf life of sprout vegetables.

Fig 1

(A) A box (A-04 Fix Box, AS ONE Corp., Osaka) to store samples (scale bar: 10 mm) and (B) Method to store vegetables under different gravity levels in a thermohygrostat. (a) Samples (e.g., mung bean sprouts) stored under simulated microgravity in a box set on the inner frame of the gravity controller (Gravite^®, Space Bio-Laboratories Co., Ltd. Hiroshima, Japan) (new treatment) (b) samples stored under normal gravity in a box (control treatment) (c) inner flame (d) outer flame (e) accelerometer (f) hygrothermograph.

Fig 2. Changes in gravity on the gravity controller (e.g., mung bean sprouts).

Full line: x axis, dashed line: y axis, chain line: z axis.

Fig 3. Typical changes in the shape of mung bean sprouts at different gravity levels (scale bar: 10 mm).

(a) a sample before the start of storage under normal gravity [mass retention rate (M_r): 100%], (b) a sample after storage under normal gravity (M_r: 5.5%), (c) a sample before the start of storage under simulated microgravity (M_r: 100%), (d) a sample after storage under simulated microgravity (M_r: 17.8%).

Fig 4

Changes in mass retention rates of (A) vegetable soybeans, (B) mung bean sprouts, and (C) white radish sprouts. Symbols are the means of ten (A, B) and six (C) measurements ± standard error. Dashed and full lines denote the data under normal gravity and simulated microgravity levels, respectively. Asterisks denote significant difference at p < 0.05 by Student’s t-test on the same day and vegetable.

Fig 5

(A) Typical linear regression for calculating mass reduction coefficients of vegetable soybeans (triangle), mung bean sprouts (circle), and white radish sprouts (square) stored under normal (closed symbols and dashed lines) and under micro- (open symbols and full lines) gravities; M_t and M_e denote the mass retention rate over the course of storage and assumed equilibrium mass retention rate, respectively. (B) Means ± ten (vegetable soybeans, mung bean sprouts) and six (white radish sprouts) measurements ± standard error of mass reduction coefficients. Closed and open bars denote the data under normal gravity and simulated microgravity levels. Asterisks denote significant difference at p < 0.05 by Student’s t-test on the same vegetable.