Food 2400 Assignment one food 2400 Guelph University, Assignments of Food science

Download Food 2400 Assignment one food 2400 Guelph University and more Assignments Food science in PDF only on Docsity!

FOOD*

Assignment # Andrea Thayer 1124476

1. a) There are many physical and chemical changes that occur during the freezing process. Freezing occurs when liquid water reaches 0 °C and water’s physical state changes into a solid state. This process is determined by a reduction in water temperature and therefore a decrease in kinetic energy and density in the water molecules changing the structure (De Man, 1999). Crystallization occurs when water transforms from a highly structured liquid to a solid hexagonal lattice pattern that involves less water molecules. Crystallization is a two- step process that includes nucleation and crystal growth. Nucleation is the first step where the nuclei of solid water form ice molecules and crystals grow around it. Heterogeneous nucleation occurs when water is super cooled and small ice crystals are added and as the temperature increases, nuclei develop around foreign particles. Because crystal size depends on the number of nuclei, smaller ice crystals would result in more nuclei and large crystals would have less nuclei. Ice crystals form quicker around freezing point and nucleation happens quicker at temperatures lower than the freezing point. Thus, by increasing the rate of cooling, small crystals will slowly form fine structures and have a high rate of nucleation, and by decreasing the cooling rate, fewer but larger crystals will form faster and have a low nucleation rate (De Man, 1999). By adding nuclei to liquids before freezing can create a finer crystalline structure known as seeding. Recrystallization can occur during the storage of frozen food and cause damage. A rise in temperature melts small crystals and a fall in temperature can cause water to reform these crystals on the surface of others causing damage to the food (Mine, 2021). Glass transition is an additional change that occurs during the freezing process and is important for stability. Glass formation can occur when water-containing food

b) The freezing process can decrease the rate of some reactions but increase the rate of other reactions. Water activity is the availability of water and frozen foods have lower water activity causing lower reaction rates (enzymes, mold, yeast, bacteria). This is because reactants are immobilized when frozen and when molecules have less kinetic energy, they move slower and are less likely to collide. However, lipid oxidation rates are an exception which are high in low water activity because of higher mobility of oxygen and free radicals in the absence of water. Freeze concentration and cellular disruption (water volume increase) can also increase reactions rates because both combine enzymes and substrates that catalyze collisions (Mine, 2021). c) Freezing can be carried out to minimize undesirable effects on food quality to prevent ice formation. Seeding can be done before freezing by adding nuclei for smaller crystal growth resulting in a finer crystalline structure that reduces cellular disruption (Mine, 2021). Food should be fast frozen at a low temperature so that smaller and finer ice crystals are formed, and the food should be stored in moisture-proof packaging. Total moisture content and water activity affect the progress of chemical and microbial activity that can lead to food spoilage. Therefore, freeze-dryed foods have a higher storage capacity due the lack of water. Cryoprotection also protects food by decreasing freeze concentration by immobilizing the dissolved solvents at the glass transition temperature. Avoid temperature fluctuations by limiting the amount the freezer is opened to prevent ice crystals from melting and recrystallizing on the surface of larger crystals (Mine, 2021).

2. a) Three regions of isotherms: Zone A (monomolecular layer): Water in this zone is the most strongly absorbed and the most immobile water found in food. This water cannot freeze and cannot serve as a solvent. Water activity in this zone is 0-0.05 (Mine, 2021). Zone B (multilayer): Water in this zone is held less strongly to the food. Water is bonded to itself, to the solute water, or through Hydrogen-bonding. This water has solvent properties and water activity in this zone is 0.05-0.76 (Mine, 2021). Zone C (capillary water): Water is the least bound and the most mobile in this zone. It is found in gels and cellular systems and is physically entrapped. It may be frozen, can act as a solvent, and will allow chemical reactions and microbial growth. Water activity in this zone is above 0.76 (Mine, 2021). b) The differences of the isotherms are related to the difference in food composition of the samples. Water activity affects stability of the sample because it’s an indication of how much water is “available” to participate in reactions and for microbial growth and the spoil of food (Mine, 2021). Therefore, foods with high moisture content and higher water activity are the most susceptible and according to the samples, jam, compared to cookies and crackers is the most susceptible to spoil. This is because jam has the highest moisture content due to its hydrophilic properties and high sugar content. The cracker and cookie are less likely to spoil due to having a lower water activity as shown in the graph. The cracker, however, have a lower moisture content than jam but higher than cookies. This indicates higher hygroscopic properties and the composition of the cracker having less margarine

References DeMan, J. M. (1999). Principals of Food Chemistry (3rd ed.). Aithersburg, Maryland: Aspen Publishers, Inc. Kim, S. S., Kim, S. Y., Kim, D. W., Shin, S. G., & Chang, K. S. (1998). Moisture Sorption Characteristics of Composite Foods Filled with Strawberry Jam. Academic Press, 31(4), 397–400. Krokida, M. K., & Philippopoulos, C. (2007, February 6). Rehydration of Dehydrated Foods. Retrieved June 4, 2021, from https://www.tandfonline.com/doi/abs/10.1081/DRT- 200054201 Mine, Y. (2021). Introduction to Food Chemistry. Retrieved from Course Content. University of Guelph. Zepp, M. (2018). Understanding the Process of Freezing. Retrieved June 4, 2021, from https://extension.psu.edu/understanding-the-process-of-freezing.