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A distinctive method of high-performance liquid calibration peak-area quantitation, called the standardless or absolute method, allows the absolute number of moles of the main amino acids found in twenty-six commercial fruit juices to be determined. The theory of the standardless model is briefly illustrated. The results found with this alternative method are compared with the reference procedure (calibration with external standards) by using difference plots and regression analysis. The presence of both systematic, constant, and proportional errors between the two methods is disclosed and discussed.

A simple, rapid, and reliable reversed-phase high-performance liquid chromatographic method for the analysis of 16 amino acids of main interest in commercial fruit juices (pear, orange, grapefruit, pineapple, peach, and apricot) is described. No sample cleanup is required. The pH of the fruit juices is adjusted to alkaline value (8.5) using 200 mM borate buffer, then amino acid is converted to stable derivatives using 9-fluorenylmethyl-chloroformate. The excess of derivatization reagent is removed by a hydrophobic amine, 1-amino-adamantane hydrochloride. The derivatization procedure is simple, fast, and described in detail. Amino acids are detected at 263 nm and eluted within 35 min. The calibration, precision (< or = 6.1%), and recovery (102% +/- 4%) of the method are reported. The conditions of separation are optimized; however, serine partially overlapped with aspartic acid. The amino acid profile of fruit juices is consistent with data from the literature.

Oxygen is a key factor in fruit pure´es browning. The use of a commercial glucose oxidase–catalase enzyme system (GOX) for oxygen removal and browning control of Golden Delicious apple and Kaiser pear pure´es during storage has been investigated. The effect of ascorbic acid and peroxidase has also been tested and results compared with control (no treatment). Colour change was quantified using the CIE L*, a*, b* system. Heating has been the unique treatment able to control the enzymatic browning of fruit pure´es, whereas GOX was the most efficient in reducing to low level the dissolved oxygen content in apple and pear pure´es (99% oxygen removed), and showed an interesting capability to control the nonenzymatic browning during fruit processing and pure´es storage. However, ascorbic acid decreased the nonenzymatic browning of fruit pure´es to a larger extent than any other chemical treatment used in this study. The Kaiser pear shows a fast enzymatic browning thus may represent a good ‘standard’ to measure browning kinetics. [Copyright &y& Elsevier]