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Food losses can occur during production, postharvest, and processing stages in the supply chain. With the onset of worldwide food shortages, interest in reducing postharvest losses in cassava has been increasing. In this research, the main goal was to evaluate biochemical changes and identify the metabolites involved in the deterioration of cassava roots. We found that high levels of ascorbic acid (AsA), polyphenol oxidase (PPO), dry matter, and proteins are correlated with overall lower rates of deterioration. On the other hand, soluble sugars such as glucose and fructose, as well as organic acids, mainly, succinic acid, seem to be upregulated during storage and may play a role in the deterioration of cassava roots. Cultivar Branco (BRA) was most resilient to postharvest physiological deterioration (PPD), while Oriental (ORI) was the most susceptible. Our findings suggest that PPO, AsA, and proteins may play a distinct role in PPD delay., This work was supported by PEC-PG ("Programa de Estudantes Convenio de Pos-Graduacao") coordinated by CAPES ("Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior"), CNPq, TWAS-Fellowship for Advanced Research and Training (FR Number 3240268144) and CIAT (International Center for Tropical Agriculture).

Colour and texture are important features of amala, a traditional thick paste obtained from dry yam flour. Tubers from eight yam cultivars were blanched at 65 °C for 20 min and dried at 40 °C for 5 days to test biochemical, thermal and pasting changes occurring during traditional yam flour processing. Blanching reduced peroxidase activity and drying reduced polyphenoloxidase activity, but total phenol content and the brown index of flour and of amala increased dramatically during the latter operations. The brown index of amala was significantly correlated with the total phenol content of the flour (r=0.84) and the peroxidase activity of the fresh tubers (r=0.75). Amylose content and starch gelatinization enthalpy remained stable. For all cultivars, drying significantly increased the onset gelatinization temperature, suggesting the occurrence of starch annealing. The latter leads to a reduction in swelling power and solubility during pasting, and hence to a lower paste viscosity.

Pineapple internal browning (IB) is a chilling injury that produces enzymatic browning associated with flesh translucency. Pineapple biodiversity allowed the investigation of how polyphenol oxidase (PPO) and peroxidase (POD) activities with their different isoforms are involved in the IB mechanism. Fruits of four varieties that expressed IB symptoms differently, Smooth Cayenne (SCay) and the hybrids MD2, Flhoran 41 (Flh 41), and Flhoran 53 (Flh 53), were stressed by cold. The susceptible varieties showed classical brown spots but different patterns of IB, whereas MD2 and controls showed no IB. Enzymatic activities were measured on fruit protein extracts and PPO and POD isoforms separated on mini-gels (PhastSystem). Only PPO activity was significantly enhanced in the presence of IB. Up to six PPO isoforms were identified in the susceptible varieties. PPO was barely detectable in the nonsusceptible variety MD2 and in controls. The number of PPO isoforms and the total PPO activity after chilling are varietal characteristics.

Bayoud, caused by #Fusarium oxysporum# f. sp.# albedinis# (Foa), is the most damaging disease of date palm in Morocco. In the present study we have investigated the effect of jasmonic acid (JA) on two defencerelated enzymes, namely peroxidases (POX) and polyphenoloxidases (PPO) in date palm seedlings root. Our data show that exogenous application of JA at a concentration of 50 [mu]M increased the activity of both enzymes. The increase of POX activity in the presence of JAwas much more important than that observed following infection with the pathogen. As compared to untreated plants, PPO activity was 2.2 and 1.3 times higher in BSTN and JHL cultivars respectively. In addition, PAGE analysis revealed increased band intensity of the major constitutive isoforms of POX and PPO in both JA-treated and Foa-treated seedlings. Close examination of symptomatic and asymptomatic plants showed that root tissues of symptomatic plants were massively colonized by Foa. Also, disease development in these plants appeared to involve a marked degradation of the host cell walls early during the process of pathogen invasion. In contrast, the presence of Foa in asymptomatic plants induced limited necrotic lesions (hypersensitive-reaction like lesions) that were probably involved in reducing the progression of the pathogen. Together, our findings indicate that JA is capable of enhancing date palm root resistance to infection by Foa via the activation of defence-related enzymes such as PPO and POX.

A postharvest treatment based on citric acid and chitosan was tested on two litchi cultivars of different provenance. Its effects on the activities of polyphenol oxidase (PPO), peroxidase (POD) and anthocyanase and on the anthocyanin content of the pericarp were measured as factors responsible for pericarp browning. The red colour of the pericarp was measured during storage of the fruit. The major anthocyanins present in both cultivars were cyanidin-3-rutinoside and cyanidin-3-glucoside. Although the concentration of cyanidin-3-rutinoside was 64% lower in the cultivar Kwai may (Guiwei) than in Wai chee (Huaizhi), this component represented more than 90% of total anthocyanins in both cultivars. The activity of PPO was six times greater in Kwai may than in Wai chee and the activity of POD was 30-times greater. The activity of POD was greater than that of PPO in both cultivars. The two cultivars, which differ in anthocyanin and oxidative enzyme compositions, responded differently to the acid and chitosan treatment, with the result that the red colour of Kwai may was better preserved during storage than that of Wai chee. This technique could be a future replacement for current sulphur treatments used to treat litchis transported by sea.

This study was undertaken to follow the kinetics of polyphenoloxidase (PPO), peroxidase (POD), and phenolic compounds during yam blanching at different temperatures and after drying and to identify by high-performance liquid chromatography (HPLC) the main phenolic compounds present in yam products. PPO activity was 50% higher in nonprocessed freeze-dried Florido (Dioscorea alata) than in nonprocessed freeze-dried Deba (Dioscorea rotundata). It decreased progressively during blanching. Forty-five percent of PPO activity remained after 50 min of blanching at 60 or 65 degrees C, whereas the POD activity dropped sharply to less than 20% of the initial activity after 10 min of blanching, whatever the blanching temperature. No anthocyanidins could be detected by HPLC at 520 nm in nonprocessed freeze-dried yam. Flavanols with a maximum absorption wavelength (lambda(max)) at 280 nm and cinnamic acid compounds with 320 nm lambda(max) were detected. Catechin was identified as the major flavanol with concentrations ranging from 0.26 to 0.41 microM g(-)(1) depending on cultivar. One cinnamic compound, ferulic acid, was identified and assessed in both cultivars (0.03-0.04 microM g(-)(1)). Total phenol, flavanol, and cinnamic contents decreased during blanching independently of temperature whereas some unresolved peaks were detected by HPLC in dried product. The latter was probably due to the consumption of coloring precursors and the appearance of polymerized or complex colored products.

In West Africa, yams are often processed into dry flour that is consumed as a thick paste (amala), the main quality attributes of which are colour, texture and taste. The traditional process consists of peeling, blanching and drying the fresh tubers. The fresh tubers may also be stored for several months before processing. This study was undertaken to test whether fresh tuber storage and pre- and post-blanching treatments (1-h storage of sliced fresh yam pieces in air or water and steeping in the blanching water, respectively) affect the physicochemical characteristics and pasting behaviour of dry yam flour produced from D. rotundata cultivars. Both pre-blanching treatments significantly reduced only peroxidase activity, while the post-blanching treatment significantly reduced polyphenoloxidase activity. Despite the effects on enzymatic activities, neither pre- nor post-blanching treatments had any significant effect on the amala brown index or the flour total phenol content. However, peak areas of three major cinnamic acid compounds, detected by HPLC, decreased continuously with steeping time after blanching, while fresh tuber storage led to a dramatic reduction in amala paste viscosity.