FOOD ENGINEERING - QUESTION 23.3 : (a) In the measurement of the browning (optical density) of fruit juice at 10 day interval, the following pairs of data are obtained with time t in days and browning or optical density (OD) : t = 0, OD = 0.05; t = 10, OD = 0.071; t = 20, OD = 0.089; t = 30, OD = 0.11; t = 40, OD = 0.128; t = 50, OD = 0.149; t = 60, OD = 0.17. (i) By using Excel or other programs, determine if such browning reaction can be characterised by pseudo zero order kinetics, with strong correlations between the data pairs of t and OD. (ii) When OD = 0.24, the shelf life T of such juice is expired. Calculate the value of T. (b) Let food cost percentage = ( food cost / food sales ) x 100. If total food cost of bread and butter are $25, food cost percentage of bread is 50 % and for butter is 50 %, find the total food sales of bread and butter.
FOOD ENGINEERING - ANSWER 23.3 : (a) (i) Excel program is used for quick graph plotting where x-axis is t and y-axis is OD. A linear graph with equation y = 0.002 x + 0.0501 with r squared value of 0.9996 could be obtained. High r squared value approaching 1 signifies strong correlations between the data pairs of t and OD for pseudo zero order kinetics. (ii) By using the equation y = 0.002 x + 0.0501, substituting y for OD and x for T, then T = (OD - 0.0501) / 0.002 = (0.24 - 0.0501) / 0.002 = 94.95 days. (b) Total food cost = c + d = $25 = 0.5 (C + D) and total food sales = C + D = (c + d) / 0.5 = 25 / 0.5 = $50 where c = food cost of bread, d = food cost of butter, C = food sales of bread, D = food sales of butter. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.
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