Improving spinach quality and reducing energy costs by retrofitting retail open refrigerated cases with doors

Authors: DE FRIAS, J. - University Of Maryland; Luo, Yaguang - Sunny; KOU, LIPING - Northwest Agriculture And Forestry University; ZHOU, BIN - University Of Maryland; WANG, QIN - University Of Maryland

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2015
Publication Date: 7/8/2015
Citation: De Frias, J.A., Luo, Y., Kou, L., Zhou, B., Wang, Q. 2015. Improving spinach quality and reducing energy costs by retrofitting retail open refrigerated cases with doors. Postharvest Biology and Technology. 31(8):114-120.

Interpretive Summary: The appeal of open refrigerated display cases for retailers can be explained by the clear and unobstructed access to products provided to consumers. However, this customer accessibility comes at the expense of higher energy costs, and potential food safety and quality issues due to large temperature fluctuations and temperature abuse. Product temperatures by the front of the case often exceed the FDA Food Code temperature requirement, with products at the back of the case near freezing. This issue cannot simply be solved by lowering the thermostat settings, as reduced temperatures in the front would come at the expense of frozen products in the back of the case. USDA-ARS scientists at the Beltsville Agricultural Research Center evaluated many options for improving temperature uniformity and product quality, and demonstrated that the installation of clear glass doors is the most cost-effective solution to this problem. The solution enables compliance with the FDA Food Code with consistently low, yet above freezing temperatures throughout the display case. Products on display following the Food Code recommendations also lasted longer, and with fewer quality defects. In addition, operational energy costs were 69% less than open-display cases. This study empowers fresh-cut processors and retailers with scientific information to improve product quality and reduce operational energy cost during retail display.

Technical Abstract: The prevalence of open-refrigerated display cases is ubiquitous in retail supermarkets, even in the face of the non-uniform temperature conditions present in these cases that may affect the quality and safety of the stored products. In this paper, the temperature variations ('T) of packaged ready-to-eat baby spinach were evaluated for an open display case and a display case with glass doors, in order to assess the advantages of this physical barrier in minimizing 'T and improving the visual quality and decay rate of the samples after four days of storage. The two 12-ft display cases were installed in the same room with the constant temperature of 21 °C and relative humidity of 72% with a thermostat setting at 0.6 °C for both cases. Results showed that the display case with doors significantly improved temperature uniformity and compliance with the U.S. Food and Drug Administration (FDA) Food Code recommendation of 5 °C or less to prevent microbial pathogen growth in packaged leafy greens. Only 1% of the temperatures readings over four days in the case with doors were non-compliant with the FDA Food Code, while 24% of the temperatures in the open case were non-compliant; mostly recorded by the front of the case. The lower temperatures and 'T of the case with doors were consistent with the higher visual quality scores (P<0.001) for the baby spinach samples recorded by trained panelists, based on a 9-point hedonic scale, at 7.2 and 6.6 for the case with doors and the open case, respectively. Differences in decay rate were significant (P<0.001) by the front of the case, with mean values of 8.8% for the open case and 5.5% for the case with doors. Furthermore, operational energy costs for the case with doors were 69% less than the open display case and the cost of door retrofits can be recouped in less than two years by energy savings alone.