Neural Network Modeling to Predict Shelf Life of Greenhouse Lettuce

Wei-Chin Lin,Glen Block

doi:10.3390/a2020623

Abstract

Greenhouse-grown butter lettuce (Lactuca sativa L.) can potentially be stored for 21 days at constant 0°C. When storage temperature was increased to 5°C or 10°C, shelf life was shortened to 14 or 10 days, respectively, in our previous observations. Also, commercial shelf life of 7 to 10 days is common, due to postharvest temperature fluctuations. The objective of this study was to establish neural network (NN) models to predict the remaining shelf life (RSL) under fluctuating postharvest temperatures. A box of 12 - 24 lettuce heads constituted a sample unit. The end of the shelf life of each head was determined when it showed initial signs of decay or yellowing. Air temperatures inside a shipping box were recorded. Daily average temperatures in storage and averaged shelf life of each box were used as inputs, and the RSL was modeled as an output. An R2 of 0.57 could be observed when a simple NN structure was employed. Since the "future" (or remaining) storage temperatures were unavailable at the time of making a prediction, a second NN model was introduced to accommodate a range of future temperatures and associated shelf lives. Using such 2-stage NN models, an R2 of 0.61 could be achieved for predicting RSL. This study indicated that NN modeling has potential for cold chain quality control and shelf life prediction.

Highlights

Harvested lettuce heads should be stored at 0°C until marketed or used [1]
In commercial practice, postharvest temperatures always vary throughout the distribution chain, and modeling on the basis of constant storage temperatures may not be suitable to commercial reality
neural network (NN) modeling is a flexible approach of dealing with situations where storage temperatures can not be held constant in commercial postharvest operations

Summary

Introduction

Harvested lettuce heads should be stored at 0°C until marketed or used [1]. Research has shown that the shelf life of lettuce stored at 0°C is 21 - 28 days, but only about 14 days when stored at 5°C [2].Pre-cooling and maintaining lettuce at low temperatures, without interruption, is one of the most important factors for prolonging post-harvest shelf life and quality. Harvested lettuce heads should be stored at 0°C until marketed or used [1]. Research has shown that the shelf life of lettuce stored at 0°C is 21 - 28 days, but only about 14 days when stored at 5°C [2]. Pre-cooling and maintaining lettuce at low temperatures, without interruption, is one of the most important factors for prolonging post-harvest shelf life and quality. Shelf life of field-grown lettuce was prolonged by rapid (vacuum) cooling immediately following harvest [3]. If pre-cooled lettuce is left outdoors at an air temperature of approximately 21°C, the core temperature can go from 0.6°C to 10°C within the same day [4]. Our preliminary results indicated that vacuum cooling improved the shelf life of commercially harvested greenhouse lettuce [6]

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Conclusion