Date of Award
Doctor of Philosophy (PhD)
Food Science and Human Nutrition
Julie K Northcutt
E Jeffery Rhodehamel
The effect of long-term frozen storage of Atlantic salmon and sliced peaches was studied to determine methods to optimize quality. The first experiment was conducted to determine the quality changes in Atlantic salmon stored at different freezer temperatures over 12 months. Fresh and pre-frozen salmon were placed in five different freezers set at –7°C, –12°C, –18°C, –29°C and –77°C and evaluated for quality at 30, 90, 180, 270 and 360 days of storage. In general, higher quality was retained to a greater extent in salmon held at –29°C and –77°C for 360 days compared to the other storage temperatures. No significant difference was observed in salmon held at –29°C and –77°C for weight loss (days 180, 270 and 360), pore size (days 270 and 360), water holding capacity, texture and TBARS (days 90, 180, 270 and 360). The predicted shelf life of freshly frozen Atlantic salmon was calculated based on the zero-order reaction model which was 269 days–7°C; 298 days–12°C; 356 days–18°C; 438 days–29°C, and 424 days–77°C. While the shelf life of pre-frozen Atlantic Salmon was 271 days– 7°C; 282 days–12°C; 351 days–18°C; 393 days–29°C; and 403 days–77°C. Based on several quality parameters having minimal variation between 4 to 9 months at home freezer temperatures, energy savings could be realized by use of higher freezer temperatures for storage of salmon.
The purpose of the second and third experiments was to determine whether freezing rates and holding temperatures influence peach quality during short- and long-term frozen storage. Fresh peaches (Prunus persica) were purchased locally, sliced dipped in 2% ascorbic acid then drained and packaged. The study was divided into two experiments, one to determine the effect of the freezing phase on peach quality and the second to determine long term frozen storage effects. For the freezing effect experiment, freshly packaged peaches were placed in freezers at different temperatures (–7°C), (–12°C), (–18°C), (–29°C) and (–77°C) then removed for testing when the core temperature of the peaches reached the temperature of all freezer temperatures. The third experiment determined the long-term holding effect on quality using both fresh and pre-frozen peaches held at (–7°C), (–12°C), (–18°C), (–29°C) and (–77°C) through 360 days. Quality measurements included freeze, thaw and weight loss, lightness, firmness, moisture content, ascorbic acid equivalent antioxidant capacity (AAEAC), scanning electron microscopy (SEM) and sensory evaluation. During the freezing phase (experiment 1), peach weight loss and surface ice crystal pore size significantly decreased with increased freezing rates. Peaches held at –77°C and –29°C maintained overall quality to a greater degree than the higher holding temperatures. However, all samples enzymatically browned when thawed, therefore, frozen peaches may best if used in the frozen state for applications where appearance is a critical factor. In general, fresh, and pre-frozen peaches at –12°C were not acceptable by the sensory panelists after 270 days of frozen storage.
The data from the third experiment on peaches has shown that fresh and pre-frozen peaches (–7°C) become discolored after two weeks of storage, and other intervention strategies to maintain quality are needed. Therefore, the fourth experiment was conducted to determine polyphenol oxidase (PPO) activity, along with changes in surface color and hydroxymethylfurfural (HMF) content in fresh and pre-frozen peach slices stored at different temperatures. Fresh peaches (F) were peeled, sliced, and subjected to one of the following treatments: (1) no treatment (N); (2) blanching in boiling (96°C ± 4°C) water (B); (3) dipping in 2% L-ascorbic acid and 2% citric acid (AC); or (4) blanching in boiling water, cooling and dipping in 2% ascorbic acid and 2% citric acid (BAC). One half of the peaches from each treatment were pre-frozen (P) to a core temperature of –20°C, while the other half of the samples were not pre-frozen. Pre-frozen and non-pre-frozen peaches from each treatment group were placed freezers set to –7°C, –9°C or –12°C and held for 21 days. After 21 days of storage, PPO activity and browning was greater in peaches stored at –7°C compared to the PPO activity and browning of peaches stored at –9°C and –12°C. Overall, lightness (L*), yellowness (b*), chroma (c*) and hue (h*) decreased while redness (a*) increased during storage. BAC peaches had less discoloration and lower PPO activity compared to peach slices exposed to other treatments. Peach color parameters lightness, yellowness, chroma showed a negative correlation with the PPO activity ranged from –0.47 to –0.98 while redness showed a positive correlation with the PPO activity ranged from 0.53 to 0.99. Non-enzymatic browning (HMF indicator) was more pronounced for blanched peaches during storage than unblanched peaches. Pretreatment of blanched peaches with ascorbic and citric acid reduced browning during 21 days at frozen storage for peaches held at –9°C or –12°C. The results from the present series of experiments demonstrated that -7°C can maintain the quality of salmon for 4 months but it is not effective to maintain the quality of sliced peaches.
Aljeddawi, Wesam, "The Effect of Freezing Rates and Storage on Atlantic Salmon and Peaches" (2022). All Dissertations. 3229.