RESUMEN
Spatial-frequency domain imaging (SFDI) has been developed as an emerging modality for detecting early-stage bruises of fruits, such as apples, due to its unique advantage of a depth-resolved imaging feature. This paper presents theoretical and experimental analyses to determine the light penetration depth in apple tissues under spatially modulated illumination. Simulation and practical experiments were then carried out to explore the maximum light penetration depths in 'Golden Delicious' apples. Then, apple experiments for early-stage bruise detection using the estimated reduced scattering coefficient mapping were conducted to validate the results of light penetration depths. The results showed that the simulations produced comparable or a little larger light penetration depth in apple tissues (~2.2 mm) than the practical experiment (~1.8 mm or ~2.3 mm). Apple peel further decreased the light penetration depth due to the high absorption properties of pigment contents. Apple bruises located beneath the surface peel with the depth of about 0-1.2 mm could be effectively detected by the SFDI technique. This study, to our knowledge, made the first effort to investigate the light penetration depth in apple tissues by SFDI, which would provide useful information for enhanced detection of early-stage apple bruising by selecting the appropriate spatial frequency.
RESUMEN
This paper reports on the measurement of optical property mapping of apples at the wavelengths of 460, 527, 630, and 710 nm using spatial-frequency domain imaging (SFDI) technique, for assessing the soluble solid content (SSC), firmness, and color parameters. A laboratory-based multispectral SFDI system was developed for acquiring SFDI of 140 "Golden Delicious" apples, from which absorption coefficient (µ a ) and reduced scattering coefficient (µ s ') mappings were quantitatively determined using the three-phase demodulation coupled with curve-fitting method. There was no noticeable spatial variation in the optical property mapping based on the resulting effect of different sizes of the region of interest (ROI) on the average optical properties. Support vector machine (SVM), multiple linear regression (MLR), and partial least square (PLS) models were developed based on µ a , µ s ' and their combinations (µ a × µ s ' and µ eff ) for predicting apple qualities, among which SVM outperformed the best. Better prediction results for quality parameters based on the µ a were observed than those based on the µ s ', and the combinations further improved the prediction performance, compared to the individual µ a or µ s '. The best prediction models for SSC and firmness parameters [slope, flesh firmness (FF), and maximum force (Max.F)] were achieved based on the µ a × µ s ', whereas those for color parameters of b* and C* were based on the µ eff , with the correlation coefficients of prediction as 0.66, 0.68, 0.73, 0.79, 0.86, and 0.86, respectively.
RESUMEN
China has abundant available marginal land that can be used for cultivation of lignocellulosic energy plants. Saccharum arundinaceum Retz. is a potential energy crop with both high biomass yield and low soil fertility requirements. It can be planted widely as cellulosic ethanol feedstock in southern China. In the present work Saccharum arundinaceum was pretreated by liquid ammonia treatment (LAT) to overcome biomass recalcitrance, followed by enzymatic hydrolysis. The monosaccharide contents (glucose, xylose, and arabinose) of the enzymatic hydrolysate were determined by high performance liquid chromatography. Experimental results show that the optimal LAT pretreatment conditions were 130 0C, 2:1 (W/W) ammonia to biomass ratio, 80% moisture content (dry weight basis) and 5 min residence time. Approximately 69.34% glucan and 82.60% xylan were converted after 72 h enzymatic hydrolysis at 1% glucan loading using 15 FPU/(g of glucan) of cellulase. The yields of glucose and xylose were 573% and 1 056% higher than those of the untreated biomass, and the LAT-pretreated substrates obtained an 8-fold higher of total monosaccharide yield than untreated substrates. LAT pretreatment was an effective to increase the enzymatic digestibility of Saccharum arundinaceum compared to acid impregnated steam explosion and similar to that of acid treatment and ammonia fiber expansion treatment.