Alternative Processing Technologies for the Control of Spoilage Bacteria in Fruit Juices and Beverages

4 Alternative Processing Technologies for the Control of Spoilage Bacteria in Fruit Juices and BeveragesPurnendu C.. Vasavada CONTENTS IntroductionControl of Microbial ContaminationPreve

4 Alternative Processing Technologies for the Control of Spoilage Bacteria in Fruit Juices and Beverages

Purnendu C Vasavada

CONTENTS

IntroductionControl of Microbial ContaminationPreventive Measures in the OrchardWashing

PreservativesPasteurizationNonthermal Alternative Processing TechnologiesHigh Pressure Processing

Pulsed Electric FieldUltraviolet LightIrradiation

MicrowavesSummary

AcknowledgmentReferences

INTRODUCTION

Fruit juices and fruit-based beverages are mildly acidic products, usuallycontaining fermentable sugars, organic acids, vitamins, and trace elements,and are subject to contamination by and growth of a variety of spoilageorganisms, notably yeasts and molds Recent reports of outbreaks of illness

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caused by the consumption of fruits or fruit juices contaminated with

Cryptosporidium1–4 have caused great concern In the aftermath of theseoutbreaks, the U.S Food and Drug Administration (FDA) has issued aguidance document to minimize microbial food safety hazards in fresh andminimally processed fruits and vegetables and mandated a Hazard Analysisand Critical Control Point (HACCP) program to achieve a 5-log reduction

of pathogenic organisms.5 The FDA also issued regulations dealing with thewarning label on any unpasteurized juices that have not received a 5-logreduction process and recently, published the Juice HACCP Þnal rule onJanuary 19, 2001.6,7

CONTROL OF MICROBIAL CONTAMINATION

Microbial contamination of fruit can occur at all stages of growth, harvesting,storage, and processing The surfaces of fresh fruits are often contaminatedwith yeasts and molds The use of over-mature, damaged, or fallen fruitcontaminated with manure from grazing animals has been implicated in

Salmonella and E coli O157:H7 outbreaks Control of microbial nation of fruit and fruit juice involves care at all stages of production,including preharvest practices of planting, growing of fruit, harvesting, post-harvest handling, washing, and cooling and storage

contami-P REVENTIVE M EASURES IN THE O RCHARD

Contamination of fruits with feces of animals such as deer,8 seagulls,9 andcattle and other ruminants10 in the orchard by direct or indirect contact should

be prevented, and fertilizing orchards with manure should be avoided.11

Using “drops” and damaged fruit increases the potential for microbiologicalcontamination, including contamination with E coli, and therefore should

be avoided.11–13 Another important source of E coli O157:H7 infections isdrinking water Waterborne transmission of E coli O157:H7 as a source ofinfection in domestic animals is a concern to human health as well Wangand Doyle14 reported that E coli O157:H7 is a hardy pathogen that cansurvive for long periods of time in water, especially at cold temperatures In

an outbreak, E coli O157:H7 was recovered from multiple water sources,including a borehole, a standpipe, and water stored in the home.15 Precautionsshould be taken when using untreated water for washing purposes

W ASHING

Washing, mechanical scrubbing, and the use of chemical sanitizers mayresult in considerable reduction in surface contamination (see Table 4.1).Peroxyacetic acid (1280 ppm) was effective in accomplishing more than a

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© 2003 by CRC Press LLC

TABLE 4.1

Effects of Different Chemicals in Reducing Bacteria on the Surface of Fruits

80 ppm a

1280 ppm b

3 5.5

1.2–2.2 4 3–4 1–2

E coli O157:H7

S chester

Strawberry Apple Apple (cut)

1.3 2.1 1–2

Chlorine phosphate buffer (Agclor

© 2003 by CRC Press LLC

TABLE 4.1 (CONTINUED)

Effects of Different Chemicals in Reducing Bacteria on the Surface of Fruits

Type of Bacteria

Log 10

Reduction

acid, glycerol, ethanol, potassium hydroxide, sodium bicarbonate, citric acid, and distilled grapefruit oil

S population (spp.) (S agona,

0.5 1.9 1.4 1.7 2.0

a Recommended sanitizer concentration.

b 16 times the recommended concentration.

Adapted from references 9, 18, 23–25

© 2003 by CRC Press LLC

5-log reduction of E coli O157:H7 on apple surface A 4.5-log reduction of

E coli O157:H7 was obtained using chlorine phosphate buffer (3200 ppm)and chlorine dioxide (80 ppm) Hydrogen peroxide (5% H2O2) was lesseffective in reducing E coli levels; however, addition of acidic surfactants(50–60ûC) caused a 3- to 4-log reduction of E coli on apple

Failure to wash fruits properly before processing is among the mainreasons for contamination in fruit juice Washing and brushing fruit beforethe juicing step is common in juice processing According to one industrysurvey, 98% of orchards surveyed washed apples before crushing, 18% used

a detergent-based fruit wash, 37% used sanitizer after washing, and 64%employed brushing in conjunction with washing.11 Winniczuk (1994)17

showed that the maximum cleaning efÞcacy of most fruit wash systemsproduces a 90 to 99% reduction in the population of microorganisms on acitrus fruit surface under optimum pilot plant situations, whereas less-than-optimum conditions may result in only a 60% reduction of fruit surfacemicroßora However, washing trials using water showed only a 1- or 2-logreduction in many experimental research studies.18,19

Conventional washing practices using chlorine and brushing only may

be partially effective in controlling microbial contamination.9 The pathogenscontaminating the fruit are not always located on the surface20 and are notalways distributed uniformly, thus limiting the effectiveness of surface treat-ments Kenney et al (2001)19 suggested that cells may be sealed withinnaturally occurring cracks and waxy cuts in platelets These cells may beprotected from disinfection and subsequently released when apples are eaten

or pressed for cider production Also, the 5-log inactivation of pathogens onthe surface may not necessarily result in requisite reduction of pathogens injuice.21,22 For example, Pao and Davis (1999)22 reported that an application

of a 5-log inactivation treatment to oranges resulted in a 1.5- to 2.0-logreduction in juice They also demonstrated that an overall 5-log inactivation

of E coli on the surface of oranges resulted in only a 3.5-log reduction inthe juice Treatment of fruit and vegetables with disinfectants is more effec-tive in removing pathogenic microorganisms than washing with water alonebut still not reliable enough to completely eliminate pathogenic bacteria

P RESERVATIVES

Another approach for controlling contamination, especially in processedproduct, is the use of preservatives In an industry survey, just 12% ofproducers reported using preservatives; among them, 60% used potassiumsorbate and 40% used sodium benzoate Potassium sorbate has little effect

in reducing E coli O157:H7 in cider.26 Although sodium benzoate wasmore effective than potassium sorbate on E coli O157:H7,26 the bacteriasurvived in refrigerated cider containing 0.1% sodium benzoate for 21

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© 2003 by CRC Press LLC

days.26 Similarly, citric and malic acids had no bactericidal effect.27 Comes

and Beelman (2002)27 indicated that a 5-log reduction of E coli O157:H7

in apple cider can be achieved using a preservation treatment involving

the addition of fumaric acid (0.15%, w/v) and sodium benzoate (0.05%,

w/v) to apple cider, followed by holding the cider at 25ûC for 6 h before

24 h of refrigeration at 4ûC The Þnal pH after the addition of fumaric acid

and sodium benzoate was between 3.2 and 3.4 The authors suggested that

this intervention process is cost effective and could easily be incorporated

into HACCP systems that are currently mandated for processing of fruit

and vegetable juices by the FDA.27

The use of preservatives may change heat resistance of E coli O157:H7

For example, potassium sorbate and sodium benzoate reduce the heat

resis-tance of E coli O157:H7, but benzoate is about eight times more effective

than sorbate.28,29 Dock et al (2000)29 stated that addition of sodium benzoate

(0.2%) increased the z-value from about 6 to 26ûC This increase may result

in a longer 5-log reduction time (higher 5D-values) at higher temperatures

(i.e., 70ûC) in cider with benzoate as compared to cider without additives

This has profound implications because processors who add benzoate to

cider before processing may obtain less than the 5-log reduction of E coli

O157:H7 that would have occurred without any benzoate addition Induction

of acid resistance can also have wide-ranging effects on the ability of bacteria

to resist other stresses such as heating, antimicrobials, and exposure to

ultraviolet light.22,30 While preservatives may have some merit for extending

product shelf life, they cannot be relied upon to eliminate pathogens from

fruit juice or cider

The FDA guideline for minimizing microbiological hazards emphasizes

Þve major areas:

By considering the potential sources of contamination and implementing

an effective combination of good agricultural and manufacturing practices

(GAPs) related to apple juice/cider production, growers can minimize the

risk of microbiological contamination

Several effective alternative processing technologies have been developed

for controlling microbial contamination, especially contamination with

pathogenic microorganisms These include pasteurization, high hydrostatic

pressure (HHP) or ultra-high pressure (UHP), ultraviolet (UV), and pulsed

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TABLE 4.2

Time–Temperature Conditions for Pasteurization of Apple Cider/Juices in the U.S

Log 10

Reduction

orange juice, white grape juice

Apple cider produced from Red Delicious apples

E coli O157:H7 (cocktail)

Adapted from Liao, C.H and Sapers, G.M., J Food Prot., 63, 876–883, 2000; Mazzotta, A.S., J Food Prot., 64, 315–320, 2001.

© 2003 by CRC Press LLC

electric Þeld (PEF).31,35,57,58 The design and implementation of HACCP andapplication of alternative processes provide the current strategy for microbialcontrol and ensuring shelf life and safety of fruit juice and beverages.5–7

pas-of the juice products In a recent survey, the majority (78%) pas-of cider ducers in Virginia indicated that they do not pasteurize their cider.16 Inanother survey, 88% of producers in Wisconsin reported that they did notheat-pasteurize their apple juice or cider.12 Also, mandatory pasteurizationmay be cost prohibitive for many smaller operations, because the costsincrease sharply as production capacity and number of days per year ofprocessing decrease.33 However, a consumer survey in Wisconsin indicatedthat 70 panelists of 192 (36%) preferred buying pasteurized cider, 32 pan-elists (17%) preferred unpasteurized cider, and 79 panelists (41%) indicated

pro-no preference.12 While there may be a preference or justiÞcation for usingalternative nonthermal processing technologies to reduce microbial contam-ination of juice, many experts believe that the use of a kill step such aspasteurization rather than prevention of contamination is the best means of

eliminating E coli O157:H7 from apple cider. 32

NONTHERMAL ALTERNATIVE PROCESSING TECHNOLOGIES

Since traditional thermal processes, though effective in inactivating bacteria,can affect the quality of the Þnished product, the scientiÞc community hasstepped up efforts to identify and review the kinetics and use of nonthermalalternative processes.31 Most notably, as a part of the Þve-year contractbetween the Institute of Food Technologists (IFT) and the FDA, a scientiÞcreview of these alternative processing technologies has considered manypertinent questions, including:

• What might be used to produce food products free from any publichealth hazard, and what are the critical control points?

• Which organism(s) of public health concern is (are) the most tant to the process(es)?

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• How do factors such as growth phase and growth conditions oforganism(s), processing substrate or food matrix, the pathogenicorganisms associated with speciÞc foods, processing conditions,storage conditions, and potential storage abuse affect the determi-nation of the most resistant organism(s) of concern for each alter-native processing technology?

• How do users determine the effectiveness of an alternative ing technology?

process-These are but a few of the signiÞcant issues being addressed TheIFT/FDA scientiÞc review of the alternative processing technologies thatmight be used for both pasteurization and sterilization includes high pressureprocessing (HPP), pulsed electric Þeld (PEF), pulsed x-ray or ultravioletlight (UV), ohmic heating, inductive heating, pulsed light, combined ultra-violet light and low-concentration hydrogen peroxide, ultrasound, Þltration,and oscillating magnetic Þelds.31 Some nonthermal alternative processingtechnologies are listed in Table 4.3

H IGH P RESSURE P ROCESSING

The use of HPP and/or ultra high pressure (UHP) as a food preservationtechnique is well documented This type of nonthermal processing is cur-rently used in various parts of the world in the manufacture of a number ofproducts, including fruit juices, fruit purees, and jams.44 HPP involves sub-jecting either packaged or unpackaged foods and beverages to pressuresbetween 100 and 800 MPa within a cylindrical pressure vessel The equip-ment used for a batch HPP system also includes two end closures withrestraints such as yoke threads, a low pressure pump, an intensiÞer that usesliquid from the low pressure pump to generate high pressure process ßuidfor system compression, and system controls and instrumentation.31 Thesebatch system steps are rearranged for use to treat unpackaged liquid foods,such as fruit juices, semicontinuously Recent studies suggest that this emerg-ing alternative technology can offer food processors a viable nonthermalapproach to ensuring food safety goals by inactivating bacteria Severalresearchers have studied the efÞcacy of various HPP treatments in inactivat-

ing microorganisms, especially the pathogens E coli O157:H7 and

Salmo-nella, in fruit juices.36,44–46 Some of these studies have shown that the lowerthe food’s pH, the higher the number of microorganisms inactivated by HPP,

as has been observed with the inactivation rates of E coli O157:H7.36 ilarly, spoilage organisms such as yeast in fruits can be effectively inactivated

Sim-by using HPP due to their inherent low pH Parish45 targeted Saccharomyces

cerevisiae in a nonpasteurized low-pH (3.7) orange juice with HPP, and a

reported D-value of 76 seconds for ascospores treated at pressures between

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© 2003 by CRC Press LLC

–2.5 V / mm, 2–20 ms, ± 150 pulses, exponential decay, <30ûC

Apple juice Apple juice

Saccharomyces cerevisiae

6 7

Salmonella typhimurium Listeria monocytogenes

5–6 7 7

35, 40

350 and 500 MPa.37 The D-values for the native ßora of the orange juiceranged from 3 to 74 seconds Yeasts and Gram-positive and Gram-negativeorganisms were found to survive 1 to 300 seconds of HPP treatment.28 Inaddition, UHP extends the shelf life of refrigerated juice by up to 30 days

if the pressures range from 44,000 to 73,500 lb/in.2 for 20 seconds to 1minute One signiÞcant problem with fresh orange juice is limited shelf lifedue to cloud loss caused by the activity of several pectin methylesterase(PME) enzymes High-pressure processing can inactivate spoilage microßoraand reduce PME activity.35

P ULSED E LECTRIC F IELD

PEF processing involves the application of high-voltage pulses for just a fewmicroseconds to food placed or ßowing between two electrodes The processdestroys both pathogens and spoilage organisms through breakdown or rup-turing the cell membrane Pores become permanent in most vegetative cellstreated above 15,000 V/cm PEF inactivates bacterial spores by reducing thedipicolinic acid needed for spore germination The components of a PEFsystem include: 31,35

• A high-voltage power supply

• An energy storage capacitor

• A treatment chamber or chambers

• A pump to conduct food though the treatment chamber(s)

• A cooling device

• Voltage, current, and temperature measurement devices

• A computer to control operations

Two commercially available systems have been used in pilot studies.31

The most common use of pulse electric Þeld processing has focused on foodpreservation and product quality aims, including extending the shelf life oforange juice, apple juice, bread, milk, and liquid eggs In fact, shelf-lifestudies show that the process can extend refrigerated shelf life of fresh citrusjuice to beyond 60 days.31 In terms of inactivating spoilage microbes in fruitjuices and fruit-based beverages, PEF has proved efÞcient in some research

In pilot experiments, researchers using PEF achieved a 5-log reduction of

E coli O157:H7 and its nonpathogenic surrogate E coli 8739 in apple cider

in 143 microseconds at a Þeld strength of 30 kV/cm and average temperature

of 25ûC (near ambient) Spoilage organisms in orange juice were reduced

by 5 logs at a peak Þeld intensity of 40 kV/cm for 60 microseconds.35 PEFtechnology also has been applied to process citrus juices in a slightly dif-ferent, energy-efÞcient low-voltage electric pulse process in which electricity

is directly pulsed into the juice Less than 1 joule per ml is applied to a

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