Abstract
The potential of near infrared spectroscopy (NIRS) in the wavelength range of 1000–2500 nm for predicting quality parameters such as total soluble solids (TSS), acidity (TA), firmness, and individual sugars (glucose, fructose, sucrose, and xylose) for two cultivars of apples (“Braeburn” and “Cripps Pink”) was studied during the pre- and post-storage periods. Simultaneously, a qualitative investigation on the capability of NIRS to discriminate varieties, harvest dates, storage periods and fruit inhomogeneity was carried out. In order to generate a sample set with high variability within the most relevant apple quality traits, three different harvest time points in combination with five different storage periods were chosen, and the evolution of important quality parameters was followed both with NIRS and wet chemical methods. By applying a principal component analysis (PCA) a differentiation between the two cultivars, freshly harvested vs. long-term stored apples and, notably, between the sun-exposed vs. shaded side of apples could be found. For the determination of quality parameters effective prediction models for titratable acid (TA) and individual sugars such as fructose, glucose and sucrose by using partial least square (PLS) regression have been developed. Our results complement earlier reports, highlighting the versatility of NIRS as a fast, non-invasive method for quantitative and qualitative studies on apples.
Highlights
Apple fruit quality is evaluated by external appearance using optical sensors on sorting machines and by destructive methods to measure internal quality traits
Significant differences (p < 0.05) between the harvest dates were found for starch index (SI), titratable acid (TA), total soluble solids (TSS), deformation associated with total puncture force (D), work associated with total puncture force (Wf), flesh limit compression force (FLC), and slope of the force-deformation curve (S) in “Braeburn” apples and for SI, TA, total puncture force (Ff), Wf, and FLC in “Cripps Pink” apples (Table 1), respectively
This study investigated the potential of near infrared spectroscopy (NIRS) as an analytical tool for the post-harvest management of fruit quality beyond present applications
Summary
Apple fruit quality is evaluated by external appearance using optical sensors on sorting machines and by destructive methods to measure internal quality traits. Non-destructive spectroscopic methods, electronic noses and electronic tongues are experiencing growing interest [9,10,11] in food science in recent years, because they are fast, easy to use, reagent free, and compatible with in-line and on-line measurement systems. Among these analytical techniques near infrared spectroscopy (NIRS) has attracted much attention [12,13,14,15,16,17]. No comprehensive data have been reported on the chemical composition of the two cultivars as well as on the spectral evaluation of the quality parameters including different harvest time-points and storage periods
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