Evaluation of volatile organic compound release in modified atmosphere-packaged minced raw pork in relation to shelf-life

Volatile organic compounds (VOCs) released from fresh meat during storage have the potential to be reliable parameters for monitoring shelf-life and/or spoilage using simple sensors. The VOC release profiles in raw, minced pork packaged under modified atmosphere (70% O2, 30% CO2) stored at 4 °C were measured on days 0, 3, 6, and 12 of storage by proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS). Additional sensory and solid-phase microextraction gas chromatography mass spectrometry/olfactometry (SPME-GC-MS/O) analyses of sample subsets allowed for a comparison of VOC profile changes with changes in sensory impressions and aided compound identification. Alcohols, aldehydes, ketones and acids were observed to change over time, either increasing continuously or decreasing after reaching maximum concentrations early to mid-way during storage. Marked differences were observed in the concentrations of several compounds between the fresh (day 0) and aged samples (day 12). Sensory analyses indicated strong increases in buttery and greasy odours, moderate increases in cheesy, vomit-like, sweaty and sour-cream-like odours, and decreases in fruity odours. The number of lactic acid bacteria (LAB), Enterobacteriaceae, pseudomonads, psychrotrophs, mesophiles, yeasts and moulds increased throughout storage. Percentage wise, LAB dominated the microbial population at each sampling point and pH decreased during storage. Values of thiobarbituric acid reactive substances (TBARS) indicated marginal lipid oxidation during the first week of storage. The present study provides useful information on the development of characteristic volatile spoilage compounds and offers insights for the potential future implementation of specific sensors to monitor shelf-life.