Impact of Special Drying Schemes on Color Stability of Mangoes with Different Maturity Degrees.

Alioune Diop,Mathieu Léchaudel,Frédéric Chiroleu,Marc Chillet,Mady Cissé,Christian Mertz,Nafissatou Diop Ndiaye,Jean-Michel Méot

doi:10.3390/foods11050656

Abstract

A previous study demonstrated that the color of 4 mm mango slices is altered very slightly by drying for 5 h at 60 °C, 30% RH and 1 m/s. The objectives of this complementary study were to determine the impact of various drying procedures encountered in the drying units on color alterations of sulfite-free mango slices from heterogeneous raw material due to variable maturity degrees of mangoes. Drying procedures with various temperature/humidity/duration combinations were performed to analyze their effects on the color of natural dried mangoes according to the degree of fruit maturity. They were dried at an air speed of 1.0 m/s for 5 h according to 3 schemes: standard drying (SD) at 60 °C and 30% RH; wet drying (WD) for 1 h at 60 °C and 60% RH, followed by 4 h SD; and finally, hot drying (HD) for 4 h SD, followed by 1 h at 80 °C and 30% RH. The color of the mango slices was analyzed before and after drying. SD preserves the color of fresh mangoes very well, whatever their maturity stage. A relatively slow drying onset corresponding to WD has a highly adverse impact, which becomes greater as the degree of maturity increases. There is already significant browning on mangoes with near-optimum quality (L* = 75; H* = 92). Applying high temperature at the end of the drying procedure (HD) for 20% of the time has a more limited adverse impact with immature mangoes that are the most sensitive. Linear regressions were assessed to represent the relationships of color differences between drying schemes according to mango maturity degrees. These statistical models showed a significant increase in color degradation in the case of WD and a decrease in color differences in the case of HD with the advance in fruit maturity.

Highlights

The ripening time to achieve a good degree of maturity for drying was 6 days from mango harvesting
This short time is understandable, since mangoes harvested at the yellow-point stage have already begun their climacteric crisis on the tree
The results obtained agree with the empirical knowledge of fruit drying operators: optimal quality cannot be obtained with a too slow drying onset due to insufficient heating power, an overloaded mango dryer or the application of a too high temperature at the end of drying performed to reduce drying duration

Summary

Introduction

The color of natural, sulfite-free mangoes changes during storage until they become undesirable and unsellable [1]. They are kept at managed temperatures by many operators, and consumers are advised to store them in the refrigerator. The two generally recognized explanations are, firstly, limited heating power and ventilation, which lead to a slow drying onset during which the surface of the mango pieces remains saturated with water, and, a development of enzymatic browning reactions on these pieces [4]. A high end-of-drying temperature, whether through ignorance or the need to accelerate water diffusion, leads to the development of Maillard reactions [5]

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Conclusion