Team:NEFU China/fit
Team:NEFU China/Description
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As one type of the
oldest fermented food, yogurt is very popular around the world. Different from
other traditional dairy products (cottage cheese, sour cream and etc.), yogurt
wins its popularity due to the health benefits it can offer. Primarily, yogurt
comes from milk and is nutritionally rich in protein, calcium, riboflavin,
vitamin B6 and vitamin B16. Additionally, Lactose-sensitive individuals may
tolerate yogurt better than other dairy products due to the conversion of
lactose to glucose and galactose, and the fermentation of lactose to lactic
acid carried out by the bacteria in the yogurt. Most importantly, it generally
possesses a certain amount of probiotics, which is necessary in our digestive
tracts.
Fig1. Delicious yogurt
In spite of these
health benefits, yogurt is easy to go bad and spoiled yogurt has more harm than
good. Last semester, one of our teammates was absent for class due to eating
some spoiled yogurt, although it was still within the expiration date.
Generally, yogurt within expiration date is safe for eating if it is always
kept cold, which was neglected by this teammate who consequently suffered from
diarrhea. As you can see, yogurt may cause food poisoning even though it has
not expired. This is one of the reasons why we came up with an idea of
developing a yogurt guarder.
We searched the
Internet for relevant information and found varieties of news about yogurt
spoilage within shelf-life. Bacteria contamination in
yogurt cannot be recognized by our naked eyes. Thus, many people may suffer
from that.
To understand why
yogurt may not be safe for eating even before the expiration date, we need to
know how yogurt is produced. First, raw milk is treated with pasteurization to
kill most microorganisms inside without destroying its nutritional components.
Second, Lactobacillus is inoculated for fermentation. Then, yogurt
is made. Unlike sterilization, pasteurization is unable to kill all
microorganisms in the food. Instead, it intends to reduce the number of
pathogens without significantly affecting nutrient. So yogurt must be kept in
cold for a limited time period; otherwise pathogenic bacteria that survive from
pasteurization can quickly grow and cause yogurt spoilage.
We did a simple
experiment to test the appearance and contents of yogurt under different
conditions. We bought fresh yogurt from the same batch and kept some of them in
fridge and some at 35¡æ for half an hour. Then, we took pictures of
them. The yogurt kept at both conditions looked the same. However, our subsequent
experiments revealed that yogurt kept at 35¡æ had a
higher number of coliform bacteria than that from the fridge and the pathogens
significantly exceeded the qualify standard. This means the pathogen contents
of yogurt may significantly increase when we carrying yogurt from a supermarket
to home, since yogurt will be exposed to ambient temperature for a while,
especially in summer. (Visit Result for more details)
Fig2. Yogurt treated with different temperature. (A) Fresh
yogurt kept in 4¡æ for 0.5hour (B) Fresh yogurt kept in 35¡æ for half an hour (C) Yogurt kept in 4¡æ until
one-day past expiration
Needless to say, no one would like to eat yogurt if he or she knows it may contain such a high amount of coliform. However, the current methods to test pathogenic bacteria generally contain multiple cumbersome steps, are time consuming and require special equipment. They obviously cannot be used in our daily life. Therefore, a handy detecting approach for pathogenic bacteria in yogurt is urgently needed.