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BłOLOGICAL AEROSOL MFASUREMENT IN DAIRY PLANTS

air during flooding, especially after being idlc ovemighi (33). The generał quality of plam sanitation. ihc location of ihc dairy. quali(y of ventilation and degree of pcrsonal hygicnc werc found by Ccma (16) to bc important faciors in determining proccssing plant air qualiiy. Hcdrick et al. (33) indicatcd that the clcanliness of the storage arca and prccautions of unpacking supplics in proccssing and pack-aging arcas arc also important.

Perry et al. (57) studied airbome contamination of chcese with lactobacilli. They sclcctivcly isolatcd and iden-tificd similar lactobacilli from the air and cheeses. “Cheese typcs’* of lactobacilli were found in the air sonie months bcforc and after the chccsc was madc, which indicatcs contamination of tire air frorn other sources within the dairy. Naylor and Sharpe (55) comparcd possible sources of lactobacilli contamination and concludcd that air was the major sourcc.

Air qualiry and shelf-life of products

Angevine (5) uscd exposed plates of pasteurized skim milk followcd by a Moseley keeping quality test (52) for estimating the air quality in a cottage cheeses processing room area. His data indicate that poor air quali(y was the cause of unsatisfactory shelf-life. In another study, the shelf-life of cottage chcese ncgatively correlated (r--0.642) with the viable particie counts of chcese proccssing room air. The cocfficient of determination indicatcd that air contamination contributed approximately 40% to the variation in shelf-life (11).

Cannon (13) did not find a relationship between airbome microbial populations and keeping quality of the packaged milk. This was probably because the contamination of milk from sources other than air was sufficient to overshadow any airbome contamination.

A spccial packaging system, the ‘long-life machinę’ (designed by Ex-CeII-0 Co., Walled Lakę, MI), encloses the niling chamber with fitted fiber glass covers and is designed to eliminatc the nced for a defoamer. This system protects products from airbome contamination and may extend the shelf-life of whole milk by 7 d. The SPC for whole milk run on this machinę did not reach 20.000 cfu/ ml for 18 d, whereas the same milk packaged by a standard machinę exceedcd 20,000 cfu/ml after 12 d (43). This dala shows the cxtent to which airbome contamination may influence the shelf-life of product madę from high quality raw milk.

RonićS of airbome product contamination

Any point at which product is cxposcd to air is a possible roulc for airbome contamination. Air for mixing raw milk hcld in silos and for removing product from pipelines is often a sourcc of contamination (41). Exposure of products at the filier and via vacuum defoamers are also important sources (15). Hor ice crcum, comprcsscd air inlroduccd for overmn and exposure during filling lead to contamination. Dry products have intimate contact with air during spray drying and instamization (36). Cottage chcese is cxposcd when open vats are used and during filling (5.11). Ripened cheeses are cxposed by using open checsc vats and during packaging. Whcncver product comcs into contact with largc volumcs of air, the air sKould be filtcrcd. Oflcn. thesc filters arc not propcrly maintained rcsulting in reduccd effective-

ness.

Proposed iguidelines of air quality in dairy processing and packaging arcas

Mosscl (53) devclopcd Ihc following formula for cal-culating ;icccptablc viable particie levels:

Limit (microorganisms per cu fi) = P/100 X NA' where P is what one regards as a significant percentage mcrea.se m the count of microorganisms being considcred; N is ihc geometrie mcan of the acccptable levcl of microorganisms in the food per g, and V is total volume of air (cu ft) passing ovcr or through l g of ihc food in the coursc of proccssing. The usefulness of this fonmula bas not becn determined.

Hcdrick (32) recommended the maximum levcls of viable paniclcs for air in various processing situations based on feasibiliiy as well as desirability (Table 7).

Radmorc et al. (62) proposcd air quality guide)ines based on data collcctcd from a simulatcd filling operation. This approach may be valuable, but the usefulness of the guidelines has not bcen dcmonstratcd. In addition, these proposcd guidelines are based upon limited data with a high degree of variability.

Importance of microbial air quality

Twoof the most important objectives of dairy processing arc maintenance of product safety and acceptable shelf-life. Thesc objcctives are closely related sińce they arc strongly influcnced by post-pasteurization contamination. Potcntial sources of post-pasteurization contamination in-clude air. the filling machinę, improperly cleaned equip-ment and wom eąuipmcnt as important possibililies. Air is usually considcred the least important of these sources. Hcdrick and Heldman (34) concluded that airbome contamination was of most importance in the manufacture of culiurcd milk products, followed by powder milk, cheese, market milk. icc cream and buuer manufaciuring in de-ercasing order of importance. Morę recently, the ice cream industry is emphasizing the control of air quality as means of preveniing contamination of product with Listeria. The FDA and Milk Industry Foundation / International Ice Cream Association (2R) recently issued guidelines for controlling environmcntal contamination in dairy plants. They indicate

1AULE 7. Kccontniended masimum levels for air in yarious processing situutions ttosed on data from a Casetla slit sampfer.

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Typcs of pmducl	Standard Piaic Couni per 10 L	Ycasi A Mold Couni per 10 L
Milk and cream	1.8	0.7
Uullcr	3.6	1.8
Dricd milk	2.8	1.8
Cultured milk and cream
and cottage chcese	1.8	1.4
Ripened checsc	3.6	4.3

JOURNAL OF FOOD FROTF.CHON. VOL 52. JULY 1989