Chapter 8, Kinetics of Chemical Reactions in Foods Video Solutions, Fundamentals of Food Process Engineering

Problem 1

Nagy and Smoot (J. Agr. Food Chem 25:135, 1977) reported the degradation of ascorbic acid in canned orange juice to be first order, and the following first-order rate constants can be calculated from their data. At $\mathrm{T}=29.4^{\circ} \mathrm{C}, 37.8^{\circ} \mathrm{C}$, and $46.1^{\circ} \mathrm{C}$, $\mathrm{k}$ in day ${ }^{-1}$ was 0.00112 , $0.0026,0.0087$, respectively. Calculate the activation energy, $\mathrm{Q}_{10}$, D value and half life at $30^{\circ} \mathrm{C}$.

Anil Kumar Singh

Numerade Educator

01:17

Problem 2

The following data were collected for the sensory change in beef stored while exposed directly to air at $-23^{\circ} \mathrm{C}$ (From: Gokalp et. al. J. Food Sci. 44:146, 1979). Sensory scores were 8.4, $6.2,5.5,5.1$ at $0,3,6$, and 9 months in storage. Plot the data and determine an appropriate form of an equation to which the data can be fitted to obtain the reaction rate constant.

Adriano Chikande

Numerade Educator

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Problem 3

Accelerated shelf life testing is often done to predict how food products would behave in the retail network. If a food product is expected to maintain acceptable quality in the retail network for 6 months at $30^{\circ} \mathrm{C}$, how long should this product be stored at $40^{\circ} \mathrm{C}$ prior to testing in order that the results will be equivalent to 6 months at $30^{\circ} \mathrm{C}$. Assume that the temperature dependence of the sensory changes in the product is similar to that for the nonenzymatic browning reaction in Table 8.1.

Victor Salazar

Numerade Educator

03:49

Problem 4

Ascorbic acid degradation in sweet potatoes at a water activity of 0.11 is first order with a rate constant of $0.001500 \mathrm{~h}^{-1}$ at $25^{\circ} \mathrm{C}$. If the $\mathrm{Q}_{10}$ for this reaction is 1.8 , calculate the amount of ascorbic acid remaining in dried sweet potato stored at $30^{\circ} \mathrm{C}$ after 3 months in storage if the initial ascorbic acid content was $33 \mathrm{mg} / 100 \mathrm{~g}$.

Sima Sarker

Numerade Educator

00:40

Problem 5

In the example problem on B-galactosidase action on lactose in acid whey, calculate the lactose conversion that can be expected using the same level of enzyme addition as in the example, if the whey is preconcentrated prior to treatment to have a lactose content of $12.5 \%$, after a treatment time of $60 \mathrm{~min}$.

Sam Limsuwannarot

Numerade Educator

03:03

Problem 6

Pectin methyl esterase in orange juice has a D value at $85^{\circ} \mathrm{C}$ of $8.3 \mathrm{~min}$. and the $\mathrm{z}$ value is $14^{\circ} \mathrm{C}$. Calculate the target juice temperature for pasteurization such that at least $99 \%$ of the enzyme will be inactivated after a 1-minute hold time followed by immediate cooling.

Nicholas Mogoi

Numerade Educator