M. Vanoli

Effects of maturity on chlorophyll-related absorption in nectarines, measured by non-destructive time-resolved reflectance spectroscopy

The ripening of fruits like nectarines and peaches is characterised by the decrease in chlorophyll content or colour of the fruit flesh. However, measuring the colour of fruit flesh is usually not conducted, as there is a lack of suitable techniques. Time-Resolved Reflectance Spectroscopy (TRS) is a novel technique that can measure the light absorbed by the fruit flesh. Using a laser light beam at 670 nm, the chlorophyll content of the fruit flesh is assessed without disrupting the natural structure of the fruit. Data on individual fruits of different maturity at harvest were analysed based on a deterministic model using mixed effect non-linear regression. The results indicate that an analysis of data combined from pre- and post-harvest is possible. Using the theory of Biological Shift Factor, an explained part of 97% is obtained at 20° C and 85% at 10° C.

The influence of harvest date on the volatile composition of ‘Starkspur Golden’ apples

Abstract The effect of harvest date on the volatile composition of ‘Starkspur Golden’ apples ( Malus domestica Borkh.) was studied. The fruits were picked 158, 172 and 181 days after full bloom (DAFB). Volatile substances were sampled by dynamic headspace on intact fruits and analysed by capillary gas chromatography. Qualitative and quantitative differences were found among the harvest dates. Apples picked 172 DAFB showed the highest amount of volatiles, as well as the best volatile composition; they had a low content of high boiling-point esters and alcohols and a high content of low boiling-point esters, which are responsible for the characteristic ‘Golden’ aroma. Apples picked 158 and 181 DAFB showed a volatile substance composition typical of immature and overripe apples, respectively.

Optical properties-microstructure-texture relationships of dried apple slices: spatially resolved diffuse reflectance spectroscopy as a novel technique for analysis and process control

The potential of spatially resolved diffuse reflectance spectroscopy in the 500-1000 nm range by means of a fiber-optics probe was investigated for acquiring scattering and absorption properties of air dried apple rings subjected to different pre-treatment conditions: without osmo-dehydration (TQ) and with osmo-dehydration for 1 (OSMO1) and 3 hours (OSMO2). The fresh apple rings were produced from ‘Golden Delicious’ apples at harvest (H) and 5 month storage at 2 conditions: controlled atmosphere (CA) and normal atmosphere (NA). Microstructure properties of the dried apple rings were also obtained from X-ray micro-CT measurements. The TQ samples were found to have significantly higher scattering properties, thicker tissue, smaller pore sizes, were less crispy, and required higher snapping work or rupture energy than the OSMO1 and OSMO2 samples. On the other hand, no significant differences were observed between the scattering properties, microstructure, and textural quality of the OSMO1 and OSMO2 apple rings. From these results, it was concluded that there is a clear process-microstructure-quality relation in osmo-air-dried apples which can be measured non-destructively with spatially resolved diffuse reflectance spectroscopy. AC C EP TE D M AN U SC R IP T ACCEPTED MANUSCRIPT 2 Therefore, this study confirmed the potential of spatially resolved diffuse reflectance spectroscopy for non-destructive quality assessment of air-dried apple slices, which provides perspectives for drying process optimization.

Changes in some odour-active compounds in paclobutrazol-treated ‘Starkspur Golden’ apples at harvest and after cold storage

Abstract Apple trees ( Malus domestica Borkh. cv ‘Starkspur Golden’) were treated 25 days after full bloom (DAFB) with paclobutrazol (PBZ) as a soil-drench application. After 2 years, fruit were picked 158 (commercial harvest), 172 and 181 DAFB from treated and untreated trees, with fruit taken at commercial harvest being stored in air at 2 °C and 90% R.H. During ripening and after 5 and 7 months of storage, treated and untreated apples were analysed for odour-active volatiles, by using either static or dynamic headspace samplings and capillary gas chromatography. The results were expressed in terms of Odour Units (Uo) in order to relate the relative importance of each compound to overall aroma. The average Uo values at harvest and after storage showed that only half of the monitored volatiles were present in concentrations great enough to contribute to overall aroma. PBZ treatment enhanced the ripening processes, which are associated with volatile evolution at harvest and after 5 months of air storage, and may have a specific effect on the metabolism of pentyl acetate and ethyl butanoate.

Optical coherence tomography (OCT), space-resolved reflectance spectroscopy (SRS) and time-resolved reflectance spectroscopy (TRS): principles and applications to food microstructures

Abstract: This chapter presents the recent developments in advanced optical methods for exploring food microstructure. The chapter first discusses the basics of light propagation in food and the main limitations of classical approaches (e.g. continuous wave near infrared (NIR), colorimetry) for the measurement of the optical properties of food. It then describes the physical principles, the technological solutions and the advantages of optical coherence tomography, and of space- and time-resolved reflectance spectroscopy. The chapter includes examples of applications and an overview of future prospects.

Relationship Between Texture Sensory Profiles and Optical Properties Measured by Time-Resolved Reflectance Spectroscopy During Post-Storage Shelf Life of ‘Braeburn’ Apples

Abstract ‘Braeburn’ apples from three harvests after 6-month storage in controlled atmosphere were measured at 670 nm by time-resolved reflectance spectroscopy (TRS), ranked on decreasing μa670 (increasing maturity), classified as less (LeM), medium and more mature (MoM), randomised into three batches per harvest and analysed after 1, 8 and 14 days of shelf life. LeM and MoM apples were measured in the 630-900 nm range by TRS, and analysed for sensory profile (firm, crispy, juicy, mealy) and pulp mechanical characteristics (firmness, stiffness, energy-to-rupture). All data were processed by Principal Component Analysis (PCA). According to sensory intensity scores, fruits were either divided into five classes (very low – VL; low – L; medium – M; high – H; very high – VH) separately for every attribute, or clustered into four groups, each one representing a specific sensory profile. The absorption spectra showed a maximum at 670 nm (chlorophyll-a) and μa670 was higher in the VH class for firm, crispy and juicy and in the VL and L classes for mealy. The scattering spectra had a decreasing trend with the wavelength increase, and μs’ values were lower in the VH class for firm and crispy, and higher in the VH class for mealy and in the VL ones for juicy. PCA underlined that μs’ values were negatively related to firmness and μa670, and that μa690, μa730, μa830, μa850 and μa900 were opposed to mealiness. PC scores differed among the four sensory profiles and increased from VL to VH classes for firmness, crispiness and juiciness and from VH to VL classes for mealiness.

Time-resolved reflectance spectroscopy for nondestructive assessment of fruit and vegetable quality

In the majority of food and feed, due to the microscopic spatial changes in the refractive index, visible (VIS) and near infrared (NIR) light undergoes multiple scattering events and the overall light distribution is determined more by scattering rather than absorption. Conventional steady state VIS/NIR reflectance spectroscopy can provide information on light attenuation, which depends both on light absorption and light scattering, but cannot discriminate these two effects. On the contrary, time-resolved reflectance spectroscopy (TRS) provides a complete optical characterisation of diffusive media in terms of their absorption coefficient and reduced scattering coefficient. From the assessment of the absorption and reduced scattering coefficients, information can then be derived on the composition and internal structure of the medium. Main advantages of the technique are the absolute non-invasiveness, the potentiality for non-contact measurements, and the capacity to probe internal properties with no influence from the skin. In this work we review the physical and technical issues related to the use of TRS for nondestructive quality assessment of fruit and vegetable. A laboratory system for broadband TRS, based on tunable mode-locked lasers and fast microchannel plate photomultiplier, and a portable setup for TRS measurements, based on pulsed diode lasers and compact metal-channel photomultiplier, will be described. Results on broadband optical characterisation of fruits and applications of TRS to the detection of internal defects in pears and to maturity assessment in nectarines will be presented.