Takahisa Matsuoka

Surface stiffness and density of eggplant during storage

Abstract Changes in surface stiffness, mass, volume and density of fresh as well as stored eggplants were studied. Storage period was varied between 0 and 168 h at 15–30 °C temperature and 90% relative humidity. Mass and volume were measured using standard methods and density was computed from them. Surface stiffness was determined using force–deformation curve obtained on uniaxial compression testing machine. Surface stiffness and volume of eggplant decreased nonlinearly till certain time of storage whereas mass decreased linearly throughout the storage period; and the density showed a reverse trend. Rate of reduction of these properties was observed maximum at 25 °C storage temperature. The storage period of 96 and 120 h were found to be critical for the eggplant stored at 30 and 20–25 °C, respectively, after which it may start rotting and may not be good enough to use them for vegetable purposes. Eggplant stored at 15 °C did not show any such sign of detoriation in the ranges of variables studied.

Precise near infrared spectral acquisition of intact tomatoes in interactance mode

To apply near infrared (NIR) spectroscopy for non-destructive quality control of intact hydroponic tomatoes, a search for precise spectral acquisition was performed. Along the equator of each fruit, six NIR spectra in the short wavelength region were acquired with a portable NIR instrument equipped with interactance fibres. Four types of spectra, which were averaged from 1, 2, 3 and 6 position(s), were calculated to be used as input vectors for dry matter calibration. The calibration results suggested that the use of 1-position spectra was not always sufficiently accurate while the 2-position spectra was acceptable. To obtain a highly efficient and stable calibration equation, the 3- or 6-position spectra should be used. By using the 6-position averaged spectra, the calibration equation with the ratio of standard deviation of reference data in validation set to standard error of prediction (RPD) of 5.05 could be obtained.

DEVELOPMENT OF FRESHNESS INDEX OF EGGPLANT

Surface gloss, stiffness, and density were considered prime contributors to the freshness of eggplant fruit (Solanum melongena L.). An index to measure freshness was defined as the ratio of product of relative spectral reflectance (surface gloss) and stiffness ratios to the density ratio. Surface gloss was measured in terms of relative spectral reflectance using a computerized spectral radiometer system. Stiffness was determined as an initial slope of force deformation curve obtained by uniaxial compression tests. Weight and volume for computing eggplant density were determined by standard methods. These parameters were changed to consumers’ acceptable limit by storing the eggplants for different periods at 25.2.C temperature and 90µ5 % relative humidity. Experiments were replicated five to eight times, and the average values were used to compute dimensionless ratios (values at any time divided by initial value) that were later used to determine a freshness index. Various forms of equations were tested for best fitting the data to establish the best relationship with price variation in local market. The freshness index of eggplant fruit decreased exponentially with storage period while it varied in form of power equation of weight and density ratios. It attained the lowest value (5.6%) at acceptable limit of weight ratio of about 0.87. Freshness index correlated linearly with stiffness ratio and quadratically with surface gloss (correlation coefficient 0.99). Price of eggplant varied linearly with the freshness index with good correlation coefficient (0.98), which indicated that the developed freshness index might be useful in estimating the price of eggplants.