Differences in Volatile Flavor Compounds in Hand-Grab Mutton Frozen at Different Freezing Rates

To investigate the influence of freezing rate on the volatile flavor compounds in hand-grab mutton, the differences in the volatile flavor compounds among unfrozen samples (control) and those frozen at three different freezing rates, namely 0.26 (-18 ℃), 0.56 (-40 ℃) and 2.00 cm/h (-80 ℃) were analyzed by headspace solid phase micro-extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and electronic nose. The results showed that the eutectic point temperature of hand-grab mutton was (-9.66 ± 0.24) ℃. In terms of overall odor perception, the electronic nose could distinguish hand grab mutton frozen at different freezing rates. Totally 44, 40, 49 and 53 volatile substances were identified in the control, -18 ℃ frozen, -40 ℃ frozen and -80 ℃ frozen samples, respectively, among which aldehydes, alcohols and ketones were the major ones. The content of total volatile substances in these frozen samples was 30.78%, 40.79% and 70.75% of that in the control group, respectively. The contents of aldehydes, alcohols, ketones, acids and esters decreased with decreasing freezing rate. For all samples, hexanal, heptanal, octanal, nonanal, (E)-2-octenal, 2,4-decadienal and 1-octen-3-ol were determined as key aroma compounds based on relative odor activity value (ROAV). The higher the freezing rate, the greater the ROAV values of these compounds. The sensory scores of the four samples followed the decreasing order of control > -80 ℃ > -40 ℃ > -18 ℃ (P < 0.05). In summary, we concluded that the freezing of hand-grab mutton can cause losses of a large number of volatile aroma components, but higher freezing rates can reduce the loss of volatile aroma components, maintaining the original flavor to a large extent.