Effects of blanching and storage on capsaicinoid stability and peroxidase activity of hot chili peppers (Capsicum frutescens L.)

Abstract

Comprising the major pungent principles capsaicin, dihydrocapsaicin and nordihydrocapsaicin, changes in capsaicinoid contents of chili powders after thermal treatment and during storage experiments were monitored. For this purpose, freshly harvested chili pods and chili pastes were immediately pasteurized at 80 °C, 90 °C and 100 °C for 5 and 10 min, respectively, and finally lyophilized. Heating and drying resulted in a 21.7% to 28.3% degradation of the initial capsaicinoid content, the three major capsaicinoids showing similar heat susceptibility. During storage at ambient temperature over 6 months with and without illumination, further degradation of the pungent principles by 6.8–11.9% was observed. Since residual enzyme activities were assumed to cause capsaicinoid losses, soluble peroxidase (POD) activity was investigated. It was shown that immediate thermal treatment of the plant material did not result in a complete POD inactivation even under rigorous temperature–time regimes. In contrast, a regeneration of about 30% of initial POD activity was found in those samples which were first blanched at 80 °C for 5 and 10 min and then minced. However, no correlation between POD activity and capsaicinoid losses could be established.

Industrial relevance

Besides microbial contamination and color properties, the pungent principles called capsaicinoids are the major quality parameters of hot chili peppers and might be influenced by peroxidase activity. The present contribution demonstrated that heating of fresh chili pods slightly diminishes capsaicinoids, which were further reduced during storage at ambient temperature irrespective of soluble peroxidase activity. The production of high quality spices characterized by low microbial load and bright color requires thermal treatment of the raw material; however, a slight decrease in capsaicinoid concentration cannot be excluded.

Introduction

Chili peppers (Capsicum frutescens L.) are one of the most important spices, widely cultivated and used all over the world. The amounts and characteristics of flavoring, coloring and especially pungent principles of Capsicum fruits are important quality parameters. Their strong pungency has been attributed to capsaicinoids, of which capsaicin and dihydrocapsaicin constitute more than 80% (Kirschbaum-Titze et al., 2002a, Topuz & Ozdemir, 2004). Their quantities vary with genotype and maturity and are influenced by growing conditions and losses after processing (Zewdie & Bosland, 2001). Several minor capsaicinoids and related compounds have also been identified (Maillard et al., 1997, Schweiggert et al., 2006, Thompson et al., 2005), but are present at very low levels and not expected to contribute greatly to overall pungency (Krajewska & Powers, 1988, Todd & Bensinger, 1977). Apart from their role as flavor ingredients, medical, toxicological and repellent applications of these compounds have also been described (Fung et al., 1982, Reilly et al., 2005, Yosipovitch et al., 1982).

Capsaicinoids are synthesized and accumulated in the epidermal tissue of the placenta (Iwai et al., 1979a, Suzuki et al., 1980). Their biosynthetic pathway is well characterized. While the vanillylamide moiety of capsaicinoids is derived from phenylalanine, the branched fatty acid moiety is originating from l-valine or l-leucine (Bennett & Kirby, 1968, Diaz et al., 2004). Capsaicin production increases with maturity until a maximum is reached, and then decreases through a rapid turnover and degradation up to 60% (Contreras-Padilla & Yahia, 1998, Iwai et al., 1979a), due to photooxidation or oxidizing enzymes. A recent study has shown that capsaicin and dihydrocapsaicin diminish after cellular disruption of the fruits, which is apparently due to temperature-dependent oxidation (Kirschbaum-Titze, Mueller-Seitz, & Petz, 2002b). There is some evidence that peroxidase (POD) isoenzymes may directly be involved in the capsaicinoid metabolism, since the vanillyl moiety of capsaicin is readily oxidized by these enzymes (Zapata, Calderon, Munoz, & Ros Barcelo, 1992). Bernal et al., 1993a, Bernal et al., 1993b suggested that PODs contribute to capsaicinoid degradation, in particular of capsaicin and dihydrocapsaicin. This hypothesis is corroborated by the fact that PODs are mainly located in the placenta and the outermost epidermal cell layers, where the capsaicinoids are also found (Bernal, de Cáceres, & Barceló, 1994).

In a previous study, an innovative process for the production of high quality spices has been developed (Schweiggert, Mix, Schieber, & Carle, 2005). After harvest the fresh plant material was immediately processed into a paste and subsequently heated for microbial and enzyme inactivation. Alternatively, blanching prior to crushing of the plant material was applied. Compared to conventional spices, the products obtained from chili, coriander, ginger, and green pepper were generally characterized by low microbial loads and improved color characteristics. The improved quality was attributed to the inactivation of deteriorative enzymes such as polyphenoloxidase and lipoxygenase. However, POD activities were retained even after rigorous time–temperature regimes had been applied (Schweiggert, Schieber, & Carle, 2005). Since regeneration of POD activity after heat inactivation is a well-known phenomenon, these enzymes may contribute to the degradation of capsaicinoids during storage and thus to a loss of pungency. Although capsaicin contents of chili powders were briefly described in the former investigation, the present study aimed at the stability evaluation of the major capsaicinoids during processing and storage for 6 months in detail. Furthermore, the impact of heat treatment on soluble POD and its residual activity during storage under illumination should be investigated.