1. How would changing the type of bread (fresh from a bakery, no preservatives v
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Question
1. How would changing the type of bread (fresh from a bakery, no preservatives versus prepackaged with preservatives) affect the results? The bread will decay faster if it doesn’t contain any preservatives.
2. Look up the pH of lemon juice and vinegar. Based on your results and your knowledge of favorable environmental conditions for fungal growth, what can you conclude about the effect of pH on growth?
3. How is it that mold appeared on your samples? (In other words, where did it come from or what is the source of the mold that grows on the samples?
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1. The bread with NO preservatives will decay and grow bread mold faster. The bread with preservatives will not decay within the experimental time scale. On the contrary, freshly baked bread will take time to grow mold and the same may appear towards the end of the experimental time frame. Generally, breads were prepared fresh and baked daily. But breads tend to lose their desirable texture, taste and fluffy texture upon storage, and eventually become susceptible to spoilage by certain fungi (molds). Certain types of bread contain natural microbial inhibitors. But today the demand of sustainable supply of bread has led to products with a prolonged shelf life, which is imparted by various chemicals and preservatives like potassium sorbate, sodium benzoate. calcium propanoate and calcium sulfate. Thus bread with NO preservatives is obviously more susceptible to spoilage compared to breads which are freshly baked and bread with preservatives.
2. Lemon Juice and Vinegar are in the pH range of 2 to 2.2, therefore very acidic. Extreme pH can affect the structure of macromolecules like DNA, protein and lipids. Extremely basic pH disrupt hydrogen bonds in DNA, denaturing them and hydrolyze lipids. Moderate changes in pH affect protein folding, by changing the ionization state of functional groups of amino acids and the hydrogen bonds within their structure, promoting denaturation, and therefore subsequent activity. Optimal pH for growth is the most favorable pH for an orgnaism to grow and reproduce. While most micro-organisms favor a neutral pH around 7 (neutrophile), extreme pH ranges are also favored by some (acidophile and alkaliphile). Most fungi tend to favor slightly acidic pH values ranging in the order of 5.0-6.0. Molds grow well over the pH range of 3-7. But some such as Aspergillus niger and Penicillium funiculosum can grow at pH ranging less than 2. Therefore lemon juice and vinegar pH conditions are congenial for bread molds.
3. Bread is a rich and desirable source of nutrients for mold, which grow profusely and turn blue-greenish (Penicillium) or black (Aspergillus). Moreover, to avoid the bread from getting dehydrated, such that it remains light or fluffy, bread is usually not stored in a refrigerator, but kept at room temperature. Room temperature is favourable for growth of many microorganisms including bread mold. Mold spores are present in millions in the air around us, using air for transmission. These spores settle on the bread, utilise its nutrients as food source and multiply. Depending upon favourable conditions for growth, molds divide profusely and sometimes double in size within a limites time.
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