Near Infrared Spectroscopy for the Control of Osmo-Air Dehydrated Apple Rings

Abstract

The aim of this work was to investigate the feasibility of near infrared (NIR) spectroscopy both in quantifying the residual water content of osmo-air dehydrated apple rings and in differentiating them on the basis of the sugar solution used in the osmotic pretreatment so identifying the osmotic syrup used. In order to achieve this, a set of products obtained by different processing conditions was created. Apple rings were dipped for different lengths of time (30, 60 and 90 min) in three different sugar solutions at the same water activity (aw = 0.90): sucrose (59% wt / wt), maltose (62% wt / wt) and a mixture (53% wt / wt) of fructose, glucose and sucrose having the same composition as apple. Air drying was then performed at different temperatures (70°, 80°, 90°C) and the obtained osmo-air dehydrated apple rings were packed in polypropylene film under vacuum in order to avoid water absorption phenomena. NIR spectra, in the range 10,000-4000 cm-1 , were recorded directly on packed apple rings using a FT-NIR spectrometer equipped with fiber optic probe. In calibrating the residual water content the coefficient of determination (R 2) was 0.93, the RPD value was 3.33 and RER value was 13.79, which could be considered, for our purposes, suitable for controlling the dehydration process. Moreover, applying a classification statistic method on NIR data, such as PLS discrimination analysis, it was also possible to identify correctly which sugar solution was used in the osmotic pre-treatment independently of the conditions used. Two-dimensional correlation analysis was also carried out, in order to investigate how the ratios between the main constituents, sugars and water, involved in the osmo-air dehydration varied as a function of the process variable used.

Near infrared (NIR) spectroscopy as a tool for monitoring blueberry osmo–air dehydration process

“…Due to its non-invasive nature, NIR has the potential to be used in on-line monitoring systems. Barzaghi, Gobbi, Torreggiani, Tornelli, and Giangiacomo (2008) applied NIR spectroscopy to the control of osmo-air dehydrated apple rings. The method appeared to be suitable to study the behaviour of the dehydrated apple rings during shelf-life in different environmental conditions and to interpret modifications during storage in connection with water-sugar binding.…”

Monitoring and Optimization of the Process of Drying Fruits and Vegetables Using Computer Vision: A Review

“…Barzaghi et al, in 2008, developed a method able to quantify residual moisture on osmo-air dehydrated apple rings and to discriminate them on the basis of the osmotic solution used as pretreatments [152]. Apple rings, prior to air drying, were dipped several times (i.e., 30, 60, 90 min) in three different sugar solutions.…”

Two-dimensional correlation spectroscopy — Biannual survey 2007–2009

“…Norén et al [46,47] used data pretreatment techniques, such as baseline correction and normalization by the area under the curve. The use of wavelet transformation is reported by Zhan et al [48], while Barzaghi et al [49] used standard normal variate (SNV) for the pretreatment of data. Aït Kaddour et al [50] also applied SNV, as well as the second derivatives, for the 2D analysis.…”

“…Barzaghi et al [49] used 2D NIR to study osmo-air dehydration of apple with sugar solutions. Correlation was observed with the dipping time, indicating that sugar and water content changed in the opposite directions, but the water loss occurred before the uptake of sugar.…”

“…The former changed the water content of the sample, while the latter changed the morphology, crystallinity, and consequently the evaporation rate. Barzaghi et al [49] used 2D NIR for osmo-air dehydration of apple with sugar solutions. Correlation was observed with the dipping time, indicating that sugar and water content vary in the opposite directions but water loss occurs before the uptake of sugar.…”