Factors Influencing the Free Amino Acid Content of Potato Solanum tuberosum L Tubers during Prolonged Storage

Abstract

Tubers of the potato cultivars Pentland Dell and Record were stored for a period of up to 40 weeks at 5°C and 10°C over four consecutive storage seasons (1989-1990 to 1992-1993). Reconditioning treatments at 20°C were also performed at early, mid and late stages in storage. T o assess the turnover of proteins during storage, tubers were analysed for free amino acid and soluble protein content. The net direction of nitrogen flow was dependent on the state of dormancy of the tuber and hence storage duration. An increase in free amino acid content commonly occurred during the latter part of storage, caused by an upturn of proteinase activity on the break of dormancy. This increased enzyme activity was probably due to de nouo synthesis of proteinases, in particular of a 47 kDa aspartic proteinase which was purified to homogeneity and shown to have a marked substrate-specificity for endogenous tuber proteins such as patatin. The rate of protein turnover increased with storage temperature, although the net direction of nitrogen flow was temperature independent. However, when nitrogen flow exhibited a distinct direction, such as the protein breakdown in Pentland Dell during late storage, this was enhanced by higher temperatures. The accumulation of free amino acids in Pentland Dell at 10°C corresponded with a deterioration of processing quality that could not be accounted for by an upturn in reducing sugar content. Despite an excess of free amino acids with respect to reducing sugars, amino acids had a probable synergistic influence on fry colour over the later stages of storage resulting in a darker colour per unit reducing sugar than in early storage. Reconditioning treatments were ineffective as a means of lowering the free amino acid pool size, these treatments operating solely through the decrease in reducing sugar content.

Use of unusual storage temperatures to improve the amino acid profile of potatoes for novel flavoring applications

“…Reports that the protein and amino acid content of potato juice may be modified substantially during storage have accumulated since 1956 (Niemann, 1956;Nowak & Skwiercz, 1975;Santarius & Belitz, 1978;Brierley et al, 1996Brierley et al, , 1997. Endogenous hydrolysis of potato storage proteins, believed to serve the purpose of mobilizing free amino acids for shoot growth, is limited by confinement of the proteases to vacuoles (Desborough, 1985;Burton, 1989;Brierley et al, 1996). The mechanical disintegration of potato tuber tissue should therefore allow all tuber proteases to act on all tuber proteins, under conditions of pH and temperature adjusted at will.…”

“…For flavoring applications, hydrolyzing potato storage proteins and deaminating the amides would both add value to the extracted juice. Reports that the protein and amino acid content of potato juice may be modified substantially during storage have accumulated since 1956 (Niemann, 1956;Nowak & Skwiercz, 1975;Santarius & Belitz, 1978;Brierley et al, 1996Brierley et al, , 1997. Endogenous hydrolysis of potato storage proteins, believed to serve the purpose of mobilizing free amino acids for shoot growth, is limited by confinement of the proteases to vacuoles (Desborough, 1985;Burton, 1989;Brierley et al, 1996).…”

“…These physiological changes lead to visible thermal browning during frying by increasing the concentrations of the principal compounds responsible for the Maillard reaction, namely, free amino acids and reducing sugars (Burton, 1989;Brierley, Bonner, & Cobb, 1996, 1997. The Maillard reaction is nevertheless the basis for essential flavor developments in major food products including chocolate, coffee, roast beef and malt (Heath & Reineccius, 1986).…”

Acrylamide reduction under different pre-treatments in French fries

“…Beside diversity in storability between cultivars, large variation is often found between different potato lots/fields of the same cultivar within and between years (Olsson, Svensson, & Roslund, 2004), and hence they should be managed accordingly. Normally, the size of the total free amino acid pool in potato tubers exceeds that of the total reducing sugar pool, and it would be expected that only the latter metabolites limit the degree of color production during storage correlated with darker fry color with an upturn in reducing sugar content (Brierley, Bonner, & Cobb, 1996).…”

Processing quality comparisons in potatoes stored under refrigerated and non-refrigerated conditions

“…Free amino acids content of tubers increased during storage (Table 1) because of increase in proteinase activity on the break of dormancy (Brierley et al 1996). Though amino acids are important substrates in the Maillard reaction, their concentrations could rarely be limiting.…”