Food Biochemistry and Food Processing (2 edition)

BLBS102-c38 BLBS102-Simpson March 21, 2012 14:17 Trim: 276mm X 219mm Printer Name: Yet to Come

740 Part 7: Food Processing

Table 38.10.Calculation of Process Time (B)Using

Stumbo Method

1 jh 0.96

2 fh 12.6 min

3 Process lethality (Fo)5min

4 Retort temperature (Tr) 245 ◦F

5 Initial temperature (Ti) 175 ◦F

6 Ih=Tr−Ti 70 ◦F= 245 − 175

7 jh∗Ih 67.2

8 Log(jch∗Ih) 1.75

9 Zvalue 18 ◦F

10 Fi= 10

( 250 −T

zr

)

1.9

11 fh/U=fh/(Fo∗Fi) 1.33

12 jcc

From Stumbo’s table forz= 18 ◦F

(18◦F) (jcc=1.6), obtaing

value by interpolation

fh/Ugvalue

1.00 0.638

1.33?

2.00 2.34

Interpolatedgvalue is 1.2 for

fh/Uvalue of 1.33

1.6

13 log g 0.0792

14 B=fh[log (jchIh)−log g)] 21.68 min

Table 38.11.Calculation of Process Lethality (F 0 )Using

Stumbo Method

1 jh 1.9

2 fh 36.2 min

3 Operator process time (Pt)42min

4 CUT 10 min

5 Retort temperature (Tr) 255 ◦F

6 Initial temperature (Ti) 160 ◦F

7 Ih=Tr−Ti 95 ◦F

8 jch∗Ih 180.5

9 Log(jch∗Ih) 2.26

10 zvalue 18 ◦F

11 Fi= 10

( 250 −Tr

z

)

0.53

12 B=Pt+42%CUT 46.2 min

12 B/fh 1.28

13 log g=log(jch∗Ih)−B/fh 0.98

14 g 9.55

15 jcc

From Stumbo’s table forz= 18 ◦F

(jcc=0.8). Obtainfh/Uvalue

by interpolation

fh/Ugvalue

10.00 8.24

? 9.55

15.00 10.16

Interpolatedfh/Uvalue is

13.41 forgvalue of 9.55

0.8

16 F 0 =fh/[(fh/U)∗Fi] 5.1 min

two effects to get a better quality safe product. This goal can be

achieved by optimizing thermal process conditions. In order to

achieve proper process optimization, accurate determination of

kinetic parameters of microorganisms, spoilage enzymes, and

quality factors are crucial. The need to optimize processing con-

ditions arises when the kinetic behavior of the different com-

ponents is considered because the rate of a chemical reaction

generally doubles for a 10◦C rise in temperature, whereas rates

of bacterial destruction increase tenfold under similar condi-

tions (Holdsworth 1985). Gathered kinetic parameters are used

to develop reliable predictive models that will ensure to produce

better quality products without compromising food safety.

There are two key issues that should be explored to pro-

duce better-quality safe products. The first choice may focus

on reducing thermal intensity levels, through reducing of the

heating, and cooling times associated with the process through

improving heat transfer property of processing condition and

modification of geometry of packaging material. The other op-

tion is to look for novel thermal or nonthermal food processing

technologies that will ensure better quality products with rel-

atively same degree of safety. New preservation technologies

are utilized because of their expected potential to inactivate mi-

croorganisms and spoilage enzymes with a very little damage

on product quality.

High-Temperature Short-Time and Ultra-High

Temperature Processing

As the names implies, high-temperature short-time (HTST) and

ultra high temperature (UHT) processes use higher tempera-

tures and shorter processing times than conventional thermal

processes to improve quality of foods and beverages. Because

the products are exposed to high temperatures for short times,

there is reduced degradation of quality factors of the products

while causing a greater effect on destruction of food microor-

ganisms.

The principle of HTST or UHT process is easily understood by

comparing the heat resistance of nutrient components, microbial

spores, and vegetative bacteria (Figure 38.9). TheDvalue at

reference temperature for vegetative bacteria are in fraction of

seconds (z= 5 ◦C); microbial spores, 0.2 minute (z= 10 ◦C); and

nutrient components, 100–150 minutes (z= 25 − 30 ◦C). This

variation gives an opportunity to optimize processing condition

for better quality production of foods and beverages.

From destruction of vegetative bacteria point of view, area (A,

B, and C) beneath the dotted line of the graph are not acceptable

(Figure 38.9). In these sections, the vegetative bacteria are not

yet destroyed. The same is true for section D, E, and F, where

the product is cooked but spore formers still survive the heat

treatment. All sections of G, H, and I above the bold line gives

sterile product. However, the question that comes here is that,

to what extent the product is cooked with respect to the quality

factors. The top and bottom brokenDlines represent 90% and

10% destruction of a nutrient component, respectively. Particu-

larly, section I of the graph gives a safe product with less than

10% destruction of nutrient. This is the region corresponding to

HTST or UHT treatment as indicated by the arrows.