Modeling pigment contributions to spectral reflection of apple fruit

Monitoring of fruit freshness using phase information in polarization reflectance spectroscopy

The control of food quality and freshness is of growing interest for both consumers and the food industry. The optical absorption and scattering properties in fruits, for example, changes with the physiological and biochemical alterations in the tissues during ripening and storage. The absorption and scattering properties are nondestructively monitored using near-infrared (NIR) spectroscopy. NIR has proved to be one of the most efficient and advanced tools for continuous monitoring and controlling of process and product quality in the food processing industry. However, NIR spectroscopy is costly and needs reliable calibration. The basic spectral feature of fruit reflectance in the visible region is considered in this work for the development of algorithms to nondestructively monitor the ripening and decay of apples using phase information of the reflected light. The objective is to develop simple and low-cost instruments that could revolutionize the on/inline quality monitoring of foods.

Physical-Chemical Composition and Quality Related Changes in "Ruaner" Pear (Pyrus ussuriensis) During Freezing-Thawing Period

“Ruaner” pear (Pyrus ussuriensis Maxim.) is a fruit crop that is frequently served frozen in China. It is a typical postharvest ripening fruit that needs to ripen after harvest before it can be eaten, and freezing–thawing is one way that pears are treated during postharvest ripening. In order to study the physical–chemical composition and quality-related changes in “Ruaner” pears that result the freezing–thawing period, “Ruaner” pears were kept in a freezer (−20 °C) for 7 days, after which they were transferred to room temperature for thawing. The color of the peel of the “Ruaner” pears changed from yellow-green to yellow and then brown. The chlorophyll content and titratable acidity (TA) decreased significantly throughout 0–12 h period. The carotenoid content tended to rise and then decrease, peaking at 3 h after thawing (HAT), while the soluble solids content (SSC), firmness, total phenolic content, and total flavonoid content all generally decreased. The composition of soluble sugars and organic acids was examined in “Ruaner” pears, and the major soluble sugars were fructose and glucose, with citric acid being the most abundant organic acid. The data suggest that freezing–thawing significantly changes firmness, water content, SSC, and TA in “Ruaner” pears. At 3–4 HAT, “Ruaner” pears have moderate hardness, high water content, low acid content, and higher total phenolic, total flavonoid, and soluble solids content. Therefore, 3–4 HAT is the best time for pears in terms of both table and processing quality.

Effect of anthocyanins, carotenoids, and flavonols on chlorophyll fluorescence excitation spectra in apple fruit: signature analysis, assessment, modelling, and relevance to photoprotection

Whole apple fruit (Malus domestica Borkh.) widely differing in pigment content and composition has been examined by recording its chlorophyll fluorescence excitation and diffuse reflection spectra in the visible and near UV regions. Spectral bands sensitive to the pigment concentration have been identified, and linear models for non-destructive assessment of anthocyanins, carotenoids, and flavonols via chlorophyll fluorescence measurements are put forward. The adaptation of apple fruit to high light stress involves accumulation of these protective pigments, which absorb solar radiation in broad spectral ranges extending from UV to the green and, in anthocyanin-containing cultivars, to the red regions of the spectrum. In ripening apples the protective effect in the blue region could be attributed to extrathylakoid carotenoids. A simple model, which allows the simulation of chlorophyll fluorescence excitation spectra in the visible range and a quantitative evaluation of competitive absorption by anthocyanins, carotenoids, and flavonols, is described. Evidence is presented to support the view that anthocyanins, carotenoids, and flavonols play, in fruit with low-to-moderate pigment content, the role of internal traps (insofar as they compete with chlorophylls for the absorption of incident light in specific spectral bands), affecting thereby the shape of the chlorophyll fluorescence excitation spectrum.