Quality assessment and multivariate calibration of 5-hydroxymethylfurfural during a concentration process for clarified apple juice

Variations in the quality of clarified apple juices subjected to a lab-scale concentration process were assessed. The processing conditions were similar to those used in an industrial three-effects evaporator: 85°C for 25 minutes during the first effect (E1), 75°C for 13 minutes during the second effect (E2) and 58°C for 20 minutes for the third effect (E3). The following parameters were measured at different times from samples of the three effects: Brix content, absorbance spectrum (200 to 670 nm), processing temperature, viscosity, pH, activity of water (Aw) and 5-hydroxymethylfurfural (HMF) concentration (measured via HPLC). The highest increase in HMF occurred during E3, reaching a concentration of 22.26 ± 1.32 mg/kg, with a Brix content of 65.93 ± 0.95. Such HMF concentrations were just below the European Food Regulation Standards. An increase of HMF correlated well with a decrease of Aw and pH. Absorbance spectral values within the UV range increased with increasing processing time, reflecting the non-enzymatic browning effect. Additionally, at measurements above 50° Brix, the effect of temperature and the Brix content had a significant effect on the viscosity. Partial least squares (PLS) regression and pre-processing data under an Orthogonal signal correction OSC + Wavelets (DWT) scenario yielded a multivariate calibration model that accurately predicted the appearance of HMF during the concentration process (R2 0.947). The proposed methodology may serve as an early warning against a critical threshold of HMF by offering a simple and fast physic-chemical analysis conventionally measured by most of the juice processing industry.