Effects of supercooling, sub-freezing, and deep-freezing pre-cooling on freshness, flavor, water-holding capacity, and microstructure of beef during EPS-based distribution

This study examined how pre-cooling temperature affects beef quality and temperature fluctuations during expanded polystyrene (EPS)-based distribution, simulated as 48 h at 25 °C followed by chilled storage at 4 °C. Beef steaks were pre-cooled to -0.5 °C (supercooling), -5 °C (sub-freezing), or -18 °C (deep-freezing) and compared with a 4 °C refrigerated control. Quality was evaluated by freshness indicators (total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), total viable count (TVC)), water-holding capacity, flavor (electronic tongue, electronic nose, gas chromatography-ion mobility spectrometry), and microstructure. Pre-cooling temperature markedly affected thermal behavior, temperature fluctuation, and quality changes during EPS-based distribution. Deep-freezing (-18 °C) was associated with the largest temperature rise (∼16 °C) and more pronounced indicators of freeze-thaw damage. Sub-freezing (-5 °C) resulted in microstructural features indicative of freezing-related structural disruption and greater drip loss. Supercooling (-0.5 °C) showed the smallest temperature increase (∼4 °C), better preserved microstructure, and maintained relatively higher freshness, flavor, and water-holding capacity. At the end of the 48 h distribution simulation, all pre-cooled groups remained below 15 mg/100 g TVB-N, while the -18 °C group had the highest TBARS and purge loss. During subsequent chilled storage, the -0.5 °C group reached the spoilage limit (20 mg/100 g TVB-N) after 96 h, compared with 72 h for the -5 °C and -18 °C groups. Overall, supercooling at -0.5 °C provided the best beef quality preservation during short-term EPS-based distribution, highlighting the importance of appropriate pre-cooling state selection for e-commerce logistics.