Page 28 - FoodFocusThailand No.188 November 2021

SPECIAL FOCUS

saturated fats. The addition of antioxidants that are recognized as safe
in amounts that do not exceed the limit provided by law and storage of
frozen food at low and constant temperature can slow down the occurrence
of rancidity.
● Changes of color The color changes of frozen meat products to
brownish is caused by the auto-oxidation of myoglobin (Purple-red) to
metmyoglobin (Brown). Packing food with as little space between food
and packaging as possible by using packaging that can prevent the
penetration of oxygen and minimizing temperature fluctuation during the
storage can help reduce the occurrence of such reaction.
● Protein denaturation The globular proteins are folded such that
their polar (Hydrophilic) amino acids are bounded outward whereas
nonpolar (Hydrophobic) amino acids are bounded toward the molecule’s
interior. When the food is frozen, the molecules of water surrounded the
protein move together to form ice crystals; only a few water molecules
remain surrounding the protein. Thus, the arrangement of protein
molecules is changed to unfold. Moreover, an increase in freeze-
concentration after freezing changes ion strength and pH, resulting in
denaturation of protein. The denaturation of protein affects the functional
properties such as decreasing solubility and water holding capacity
capability and inactivating some enzymes. The use of cryoprotectants
such as sucrose, sorbitol, and polydextrose (Tomaniak et al., 1998) has
been shown to reduce the denaturation of the protein in frozen food.
● Freeze-cracking Freezing of food using a very fast freezing rate Quality Changes During Thawing Process
such as cryogenic freezing may cause freeze-cracking. This is because ● Drip loss Freezing of food using a slow freezing rate causes the
when water turns to ice, its volume increases. The rapid freezing of formation of large ice crystals that can destroy some of the food’s tissues.
water in food causes a sudden expansion of the volume resulting in When the frozen product is thawed, the water resulting from the melting
cracking. Freezing of food using a suitable freezing rate, pre-cooling of of the ice crystals will separate from the food’s tissues, causing a drip
food before freezing and reducing the moisture content of food before loss. Besides the effect of the freezing rate, the temperature fluctuation
freezing can minimize the freeze-cracking of frozen food (สงวนศรีี และ during storage also causes an increase in drip loss as a result of changes
คณะ, 2556). in the size and shape of the ice crystals. The drip loss after thawing not
only decreases the weight of food but also leads to the loss of soluble
Quality Changes During Storage Process nutrients. Therefore, fast freezing of food which results in less tissue
● Freezer burn Freezer burn is the appearance of dry and pale damage due to the formation of small ice crystals, and temperature
frozen food surface and may be wrinkled, causing sticky texture and fluctuation control during storage can help reduce the drip loss of frozen
changes in flavor. This is caused by the loss of moisture during the food. However, it must be taken into account of the freeze-cracking
long-term storage of food. Moreover, the fluctuation of temperature phenomenon in case of using very fast freezing rate.
during the storage of frozen food induces the occurrence of freezer ● Enzymatic browning reaction Enzymes that inactivated during
burn. Freezer burn often occurs along with the build-up of ice crystals freezing can re-activated during thawing, leading to the occurrence of
on the internal wall of the packaging or the surface of frozen food. chemical reaction. Enzymatic browning reaction is most common in frozen
Freezer burn can be minimized by packing the frozen food in packaging and thawed fruit. The oxidation of phenolic compounds catalyzed by
that can prevent the water vapor permeability, reducing the temperature enzyme polyphenol oxidase generates the brown substances. Therefore,
of food after cooking before sealing the package in order to reduce the using an antioxidant such as ascorbic acid or adjusting the pH to an
amount of steam that will be generated in the packaging, packing food inappropriate range for the enzymatic reaction can minimize the
with as little space between food and packaging as possible and storing occurrence of browning reaction.
the frozen food under constant temperature with minimal temperature Freezing of food using a suitable freezing rate and keeping the frozen
fluctuation. food under constant temperature with minimal temperature fluctuation
● Changes in appearance and texture The temperature are the key to minimizing changes in the quality of frozen food products,
fluctuation during the storage of frozen food causes changes in the size making the products of high quality and acceptable to consumers.
and shape of ice crystals to become larger crystals. It is called ice
recrystallization. This phenomenon affects the appearance and texture
of frozen foods, e.g., ice cream with coarse texture and fruit and
vegetable with soft and mushy texture after thawing. Minimizing the
temperature fluctuation during storage and the addition of hydrocolloids
(Yuennan et al., 2014) can reduce the appearance and texture changes More Information Service Info C001
of frozen food due to the reduction of ice recrystallization phenomenon.
Chemical reactions generally occur slowly at low temperatures. เอกสารอ้างอิง / References
However, during the long-term storage of frozen food, some chemical สงวนศรีี เจรีิญเหรีียญ.2558.เทคโนโลยีการีแช่่แข็็งอาหารี. เอเช่ีย ดิิจิตอลการีพิิมพิ์ จำากัดิ,
reactions might occur. This is because small molecules of solute are กรีุงเทพิฯ.
still able to move in the freeze-concentration part (สงวนศรีี, 2558). สงวนศรีี เจรีิญเหรีียญ กานดิา ข็ันธรีาม พิรีทิพิย์ ดิาวรีาย กฤติยา วีรีะธรีรีม และวรีุฒน์
● Rancidity The oxidation of fat results in rancidity. Meat that is เจรีิญรี่�น.2556.การีแตกข็องช่ิ�นมะละกอแช่่แข็็ง:ผลจากอัตรีาการีแช่่แข็็ง ปรีิมาณข็องแข็็งที�
high in fat content and high in unsaturated fats can be more rancid than ละลายไดิ้ทั�งหมดิ และข็นาดิข็องช่ิ�น.วารีสารีอาหารี43(2):67-73.
meat with lower fat content or meat that contains higher saturated fats. Tomaniak,A.,Tyszkiewicz,I. and Komosa,J.1998.Cryoprotectants for frozen red meats.
This is because unsaturated fats are more susceptible to oxidation than Meat Sci.50(3):365-371.
Yuennan,P.,Sajjaanantakul,T.andGoff,H.D.2014.Effect of okra cell wall and polysac
28 FOOD FOCUS THAILAND NOV 2021 charide on physical properties and stability of ice cream.J.Food.Sci.79(8):E1522-E1527.

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