Comparative Evaluation of Juices from Red-Fleshed Apples after Production with Different Dejuicing Systems and Subsequent Storage

In this work, two vintages (2019 and 2020) of red-fleshed ‘Weirouge’ apples were processed with the innovative spiral filter press technology to investigate juice production in an oxygen-reduced atmosphere. After pressing, a more brilliant red color and appreciably higher amounts of oxidation-sensitive constituents (ascorbic acid, anthocyanins, and colorless (poly)phenols) were seen in spiral filter pressed juices compared to those produced with conventional systems (horizontal filter press and decanter). In a subsequent stability study (24 weeks storage at 4, 20, and 37 °C), the color and phenolic compounds were monitored and differences in the juices produced with the different pressing-systems were widely maintained during the storage period. The analyses of the anthocyanins and colorless (poly)phenols were conducted by UHPLC-DAD-ESI-QTOF-HR-MS/MS and UHPLC-DAD. The spiral filter press emerged as a promising technology for the production of juices with a more attractive color and a better retention of oxidation-sensitive constituents during processing and storage compared to conventional juices.

Determination of adulteration in apple juice by HPLC with novel optical rotation detector

A simple HPLC method for the determination of adulteration in apple juice was developed. The method is based on the detection of D-malate, derived from racemic malic acid, which is added as an acidulant. A variable-wavelength optical rotation detector was used to determine the enantiomeric excess (ee). Using anion-exchange chromatography with a phosphate buffer eluent and UV (210 nm) detection, the limit of detection for L-malate was 2 microg. With an injection of 13.4 microg of malate, the standard deviation of the ee calibration curve was 2.5%. Several apple juice samples were analyzed according to the proposed procedure, and the results agreed with those obtained using enzymatic kits for food analysis.

Enantiomeric purity determination of malic acid in apple juices by multi-beam circular dichroism detection

A multi-beam circular dichroism (CD) detector which is easily constructed by inserting inexpensive optics into a conventional photo-diode array detector has an advantage of simultaneous detection of the absorbance and CD. The enantiomeric purity determination of malic acid in beverages was performed by this detection system. Malic acid when complexed with Cu(II) was found to have an absorbance maximum at around 750 nm. The L-malic acid-Cu(II) complex showed a positive Cotton effect in its absorbance band and its anisotropy factor (delta epsilon/epsilon) was relatively large at about 1/170. This complex was retained on a reversed-phase column with the addition of racemic 2-hydroxy-3-methylbutyric acid to the mobile phase as the ligand. A plot of the relative peak areas between the CD and the absorption (delta abs/abs) versus optical purity showed good linearity with a correlation coefficient of 0.999, and the precision expressed as the relative standard deviation of the errors from the regression line was +/-2.7% (2sigma). The accuracy of the proposed method was assessed by capillary electrophoresis. Eight commercially available juice products were analyzed using this method. Five of them were thought to be adulterated with synthetic malic acid.