Optimization of Short-Term Hot-Water Treatment of Apples for Fruit Salad Production by Non-Invasive Chlorophyll-Fluorescence Imaging.

Werner B Herppich,Tina Kabelitz,Karin Hassenberg,Marco Maggioni,Susanne Huyskens-Keil

doi:10.3390/foods9060820

Abstract

For fresh-cut salad production, hot-water treatment (HWT) needs optimization in terms of temperature and duration to guarantee a gentle and non-stressing processing to fully retain product quality besides an effective sanitation. One major initial target of heat treatment is photosynthesis, making it a suitable and sensitive marker for HWT effects. Chlorophyll fluorescence imaging (CFI) is a rapid and non-invasive tool to evaluate respective plant responses. Following practical applications in fruit salad production, apples of colored and of green-ripe cultivars (‘Braeburn’, ‘Fuji’, ‘Greenstar’, ‘Granny Smith’), obtained from a local fruit salad producer, were hot-water treated from 44 to 70 °C for 30 to 300 s. One day after HWT and after 7 days of storage at 4 °C, CFI and remission spectroscopy were applied to evaluating temperature effects on photosynthetic activity, on contents of fruit pigments (chlorophylls, anthocyanins), and on various relevant quality parameters of intact apples. In ‘Braeburn’ apples, short-term HWT at 55 °C for 30 to 120 s avoided any heat injuries and quality losses. The samples of the other three cultivars turned out to be less sensitive and may be short-term heat-treated at temperatures of up to 60 °C for the same time. CFI proved to be a rapid, sensitive, and effective tool for process optimization of apples, closely reflecting the cultivar- or batch-specificity of heat effects on produce photosynthesis.

Highlights

The fact that fruit skin remains on apple slices prepared for fruit salads [1] increases the risk of microbiological contamination because microbes, including human pathogens, are naturally located on product surfaces [2]
One day after hot-water treatment (HWT) and after 7 days of storage at 4 ◦ C, chlorophyll fluorescence imaging (CFI) and remission spectroscopy were applied to evaluating temperature effects on photosynthetic activity, on contents of fruit pigments, and on various relevant quality parameters of intact apples
In apples of all four cultivars, the potential maximum photochemical efficiency of photosystem II (PSII), Fv /Fm, started to significantly decline when the HWT temperature was increased above a certain threshold, even at the short-term duration of only 30 s (Figure 1)

Summary

Introduction

The fact that fruit skin remains on apple slices prepared for fruit salads [1] increases the risk of microbiological contamination because microbes, including human pathogens, are naturally located on product surfaces [2]. HWT may even improve maintenance of fruit quality in storage [5,6,7,8] and is suitable for both conventional and organic products [9,10]. This technique has been recommended for fresh-cut fruit salad production; here, HWT needs adaptation [11].

Methods

Results

Discussion

Conclusion