Development of Authenticity Methods for Apple and Pear Juices

Abstract

Due to its widespread global consumption and economic value, fruit juice is a common target for adulteration through debasing by unscrupulous producers. Two common methods of fruit juice adulteration are debasing with commercial sweeteners and juice-to-juice adulteration. The overarching goal of this research was to develop methods to detect the undeclared addition of less expensive commercial sweeteners to pear juice and the undeclared addition of apple to pear and pear to apple juice. Methods to detect the undeclared addition of high fructose corn syrup (HFCS), hydrolyzed inulin syrup (HIS) and total invert sugar (TIS) to commercial pear juice were developed through oligosaccharide profiling employing high performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) and capillary gas chromatography with flame ionization detection (CGC-FID). Based on the application of these methods to intentional pear juice debasing, these three commercial sweeteners could be detected at levels of 0.5-3.0% (v/v). Coupled with the developed authenticity analysis for pear juice, the developed profiling methods were used to examine the carbohydrate/oligosaccharide profile of pear juice as a function of commercial processing. Chromatographic results showed that the majority of carbohydrate/oligosaccharide formation occurred during the mashing stage of juice production where enzymes (i.e. pectinases, hemicellulases and amylases) are employed. The remaining processing stages were found to have a minimal impact on the carbohydrate/oligosaccharide profile of commercial pear juice. Methods for the detection of juice-to-juice debasing between apple and pear juices were developed using phenolic profiling. High performance liquid chromatography with photodiode array detection (HPLC-PDA) was used to determine the phenolic profiles of commercial apple and pear juice concentrates from major world production regions. The phenolic profiles were used to identify fingerprint compounds for use in juice-to-juice adulteration detection. One phenolic marker was identified in apple juice and two in pear juice (excluding arbutin). These compounds were analyzed by UV-vis and NMR spectroscopic methods, and high resolution MS and LC-MS/MS spectrometry. Results from these analyses identified the fingerprint compounds as 4-O-p-coumarylquinic acid in commercial apple juice, and isorhamnetin-3-O¬-rutinoside and abscisic acid in commercial pear juice. The total phenolic content and antioxidant activities of the 27 apple and 32 pear juices used throughout this research were determined by the Folin-Ciocalteu (total phenolic content), HPLC-PDA (total phenolic chromatographic index), Trolox equivalent antioxidant activity (TEAC) and DPPH methods. The total phenolic content of apple and pear juices were found to be 294.7 ± 128.2 and 246.4 ± 45.1 ppm GAE and the total phenolic chromatographic indices were 128.8 ± 44.9 and 211.7 ± 57.2 ppm, respectively. The TEAC of apple and pear juices were found to be 130.8 ± 60.8 and 150.8 ± 63.9 mM Trolox/100 mL, while the DPPH radical scavenging abilities were 21.5 ± 12.1 and 13.6 ± 5.5 mL of DPPH/mL of juice, respectively.