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Effects of Va rying Hom ogenizat ion Pressure onthe Physical Propert ies of V an il la Ice Cream

K . A , S C H M I D T a n d O . E . S M I T HU n i v e r s i ty o f M i n n e s o t aD e p a r t m e n t o f F o o d S c ie n c e a n d N u t r i t io n1 3 3 4 E c k le s A v e n u e

S t . P a u l 5 5 1 0 8A B S T R A C T

T h i s s t u d y w a s d o n e t o d e t e r m i n e h o wv a r i o u s h o m o g e n i z a t i o n c o n d i t i o n s a f f e c tt h e p h y s i c a l p r o p e r t i e s o f a 1 0% m i l k f a tv a n i l l a i c e c r e a m . T h e h o m o g e n i z a t i o np r e s s u r e s s t u d i e d w e r e d o u b l e s t a g e2 8 1 - 3 5 ; 1 4 1 - 3 5 , 7 0 - 3 5 ; 3 5 -3 5 k g / c m 2( 4 0 0 0 - 5 0 0 , 2 0 0 0 - 5 0 0 , 1 0 0 0 - 5 0 0 , a n d5 0 0 - 5 0 0 p s i ) a n d s i n g l e s t a g e 2 8 1 ; 1 4 1 ;7 0 a n d 3 5 k g / c m 2 ( 4 0 0 0 , 2 0 0 0 , 1 0 0 0 ,a n d 5 0 0 p s i) . A n u n h o m o g e n i z e d s a m p l ew a s a l so i n c l u d e d . E x p e r i m e n t a l s a m p l e sm a d e w i t h o u t a n e m u l s i f ie r w e r e c o m -p a r e d t o a r e fe r e n c e s a m p l e , h o m o g e n i z e da t 1 4 1 - 35 k g / c m 2 ( 2 0 0 0 - 5 0 0 p s i ) c o n -t a i n i n g a n e m u l s i f i e r s y s t e m . F a c t o r sm e a s u r e d i n c l u d e d g l o s s, o v e r r u n , s ti f f -n e s s , f a t d e s t a b i l i z a t i o n , a n d m i x v i s c o s i t y .A l l e x p e r i m e n t a l s a m p l e s w e r e d e t e r-m i n e d t o b e t h e s a m e a s t h e r e f e r e n c es a m p l e f o r o v e r r u n a n d s t i f f n es s . D i f f e r -e n c e s w e r e f o u n d f o r g l o s s w i t h 2 8 1 - 3 5a n d 2 8 1 k g / c m 2 ( 4 0 0 0 - 5 0 0 a n d 4 0 0 0 p s i )s a m p l e s r a t e d a s g l o s s i e r t h a n t h e r e f e r -e n c e s a m p l e . D i f f e r e n c es w e r e f o u n d f o rf a t d e s t a h i l i z a t i o n , t h e 2 8 1 - 3 5 a n d 2 8 1k g / c m 2 ( 4 0 0 0 - 5 0 0 a n d 4 0 0 p s i ) s a m p l e ss h o w i n g l es s f a t d e s t a b i l i z a t i o n a n d t h eu n h o m o g e n i z e d s a m p l e m o r e f a t d e st a b i li -z a t i o n t h a n t h e r e f e re n c e s a m p l e . F o r m i xv i s c o s i t y , t h e 2 8 1 - 3 5 k g / c m 2 ( 4 0 0 0 - 5 0 0p s i ) s a m p l e w a s l e ss v i s c o u s t h a n t h er e f e r e n c e s a m p l e .

Received Oc tobe r 8, 1987.Ac cepted Septembe r 1 , 1987 ., Published as Pa per N um ber 15, 631 of the Scien-t i f ic Journal series of the Minneso ta Agr icu l tura l Ex-p e r imen t S t a t i o n o n research conducted under Min-neso ta Agr icu l tura l Exper iment Sta t ion Pro jec t Num-ber 18-24, supported by Hatch funds. The Universityo f Minnesota Computer Center a lso suppl ied fundingf o r t h e research.

I N T R O D U C T I O NI n t h e 1 9 2 0 ' s , R e i d e t a l . ( 8 , 9 ) s t u d i e d t h e

e f f ec t s o f h o m o g e n i z a t i o n o n t h e q u a l i ty o f i c ec r e am . T h e i r r e s u lt s s h o w e d t h a t h o m o g e n i z a -t i o n , a p r o c e s s w h e r e p r e s s u r e i s a p p l i e d t o al i q u i d s y s t e m , i s n e c e s s a r y t o p r o d u c e a h ig hq u a l i t y i c e c r e a m . T h e s e e a r l y w o r k e r s d e f i n e dh i g h q u a l i t y i c e c r e a m a s h a v i n g d e s i r a b l ew h i p p a b i l i t y , p r o p e r a i r i n c o r p o r a t i o n , p r o p e ro v e r r u n , a n d a v i s c o s i t y t h a t w a s n o t t o o t h i c ko r t o o t h i n . W i t h p r o p e r h o m o g e n i z a t i o n ,u n i f o r m b r e a k d o w n o f f a t g l o b u l e s o c c u rs ,e n s u r i n g t h a t t h e i c e c r e a m m i x a n d r e s u l t i n gi c e c r e a m h a v e t h e d e s i r a b l e v i s c o s i t y , o v e r r u n ,a n d w h i p p a b i l i t y .B a s e d o n t h e i r s t u d i e s , t h e s e i n v e s t i g a t o r s r e -c o m m e n d e d d o u b le - s ta g e h o m o g e n i z a t i o n w i t hs e t t i n g s o f 1 7 6 k g / c m 2 [ 2 5 0 0 p o u n d s p e rs q u a r e i n c h ( p s i ) ] o n t h e f i r s t s t a g e a n d 3 5k g / c m 2 ( 5 0 0 p s i ) o n t h e s e c o n d s t a g e . W i t ht h e s e p r e s s u r e s , a h ig h q u a l i t y i c e c r e a m w o u l db e p r o d u c e d . T h e s e p r e s s u r e s a r e s t i ll r e c o m -m e n d e d f o r t h e ic e c r e a m m i x m a n u f a c t u r i n gi n d u s t r y t o d a y ( 1 ) .I n 1 9 4 9 , S n y d e r ( 1 1 ) p r o p o s e d t h e i n c o r -p o r a t i o n o f c o m m e r c i a l l y p r e p a r e d e m u l s i fi e rsi n t o i c e c r e a m m i x . H e r e c o m m e n d e d u s in g av a r i e t y o f e m u l s i f i e rs ; s u c h a s m o n o - a n dd i g l y c e r i d e s , p o l y s o r b a t e s , a n d t w e e n s . H et h e o r i z e d t h a t u s i ng e m u l s i fi e r s w o u l d d i s p e rs ef a t b e t t e r , w h i c h w o u l d r e s u l t i n a m o r e s t a b l em i x e m u l s i o n a s w e l l a s a m o r e s t a b l e ic e c r e a mp r o d u c t . A l s o , e m u l s i f i e r s w o u l d a l l o w f o rp r o p e r a ir i n c o r p o r a t i o n a n d d is c o u r a g e f a tc l u m p i n g a s t h e i c e c r e a m i s f r o z e n , t h e e n dr e s u l t b e i n g a h ig h q u a l i t y i c e c re a m .

I n 1 9 5 8 , K e e n e y a n d J o s e p h s o n ( 4 ) i n v e s t i-g a t e d t h e f u n c t i o n o f c o m m e r c i a l l y p r e p a r e de m u l s i f i e r s i n i c e c r e a m . T h e y f o u n d t h a t , a st h e p r o d u c t w a s f r o z e n i n t h e b a t c h f re e z e r ,e m u l s i f i e r s a i d e d t h e f a t d e s t a b i l i z a t i o n in t h ei c e c r e a m . W h e n a n e m u l s i f i e r w a s u s e d i n t h ei ce c r e a m m i x , t h e f a t g l o b u l e s w o u l d c l u m pt o g e t h e r f a s t e r, f o r m i n g s m a l l c l u s te r s , a n d t h e

1 98 9 J Da i r y Sc i 7 2 :3 7 8 - 3 8 4 3 7 8

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HOMOGENIZATION PRESSURE EFFECTS ON ICE CREAM 3 79ice cream discharged from the ice cream freezerwas "drier" and "stiffer". These two propertiesare indicative of a good ice cream product.Other physical properties monitored on icecream included the ice cream mix viscosity,surface tension, fat destabi lization, and overrun.

Most of Keeney and Josephson's work wasdone with batch freezers. With a batch freezer,dwell time can be manipulated so that theoptimal amo un t of fat destabilizat ion occurs,producing a high quality ice cream. In a contin-uous ice cream freezer, dwell times are not soeasily changed to produce optimum fat de-stabilization (2). Thus, emulsifiers are used toenhance fat destabilization. Because homogeni-zation settings can also affect fat globule sizeand distribution, it has been suggested (5, 12)that different pressures may be used to enhancethe fat destabilizati on process, thus loweringprocessing or ingredie nt cost. Therefore, thisstudy was undertaken to determine if ice creamwithout added emulsifiers and processed atdifferent homogenization pressures would havecomparable physical qualities to ice creammanufactured by contemporary procedures andingredients.

M A T E R I A L S A N D M E T H O D SHomogenization Pressures

To investigate the effects of changes inhomogenization pressure on the physicalcharacteristics of vanilla ice cream, a variety ofhomogen izatio n settings were selected as shownin Table 1. Double-stage, single-stage, and nohomogenization treatments were studied. Thereference treatment, representing a product

made u nder normal manufacturing conditions,was defined as having double-stage homogeniza-tion at pressu re o f 141 and 35 kg/cm 2 (2000-500 psi) on first and second stages, respectively,and contai ning a commercially prepared emulsi-fier.Product

Minimum fat vanilla ice cream products ofthe compositions shown in Table 2 were usedfor the experimental and reference ice creams.The only differences between the two formula-tions were t he use of a commercially preparedemulsifier (80% mono- and diglycerides and20% Polysorbate 80) and the decrease in theamount of water blended into the mix (tocompensate for the emulsifer) in the referencesample.Processing. Ingredients were weighed, mixed,and heated to 43C. Thirty-two kilograms ofmix were removed from the initial 320-kgbatch, and the emulsifier was incorp orated intothis sample. Each batch was pasteurized at68.3C for 30 min. After pasteurization, themixes were homogenize d at the stated pressureson a Manton Gaulin homogenizer (Model12583MF12A-8DSM Everett, MA). Followinghomogenization, mixes were cooled on asurface heat exchanger to 3C, collected into37.3-L stainless steel milk cans, and placed in aIC cooler for 2 to 3 h. Mixes were flavoredwith a Category II vanilla extra ct (Gold LabelVanilla-Vanillin Extract, Northville Labora-tories Inc., Northville, MI). Mixes were frozenin random order in a Cherry Burrell (ModelV-301 Cedar Rapids, IA) continuous freezer.Ice cream samples were packaged in two 1.89-L

TABLE 1. Homogenization pressures used to process ice cream mixes.Treatments Conditions ISingle-stagehomogenization 281 141 70(no emulsifier added)Double-stagehomogenization 281-35 141-25 70- 35(no emulsifier added)Unhomogenized Pumped through the homogenizer without pressure appliedReference 141-35 (emulsifier added)

35

35-35

1All pressures are kg/cm~

Journal of Dairy Science Vol. 72, No. 2, 1989

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3 8 0 S C H M I D T A N D S M I T HT A B L E 2 . I c e c r e am f o r m u l a t i o n s s u b j e c t e d t o v a r i o u s h o m o g e n i z a t i o n p r es s u re s .I n g r e d i e n t E x p e r i m e n t a l R e f e r e n c e

(% )Seru m so l ids a 11% 11%F a t 2 1 0 . 2 % 1 0 . 2 %Sugar a 13% 13%C o r n s y r u p s o l i d s 4 4 % 4 %Stab i l i ze r s . 25% .25%Em uls i f i e r 6 .0% .075%W a t e r 6 1 . 5 % 6 1 . 4 7 %

1N o n f a t d r y m i l k , M i d A m e r i c a D a i r y m e n I n c . , S p r in g f i e l d , M O .2 C r e a m , f r e s h p a s t e u r i z e d , K o h l e r M i x S p e c i a l ty , W h i t e B e a r L a k e , M N .3 B e e t s u g a r , A m e r i c a n C r y s t a l S u g a r C o . , M o o r h e a d , M N .4 D r y c o r n s y r u p s o l i d s 3 6 d e x t r o s e e q u i v a l e n t , G r a i n P r o c e s s in g C o ., M u s c a t i n e , I A .5 L o c u s t b e a n g u m 4 5 % , g u a r g u m 4 5 % , c a r b o x y m e t h y l c e l l u l o s e 1 0% , G e r m a n t o w n M a n u f a c t u r i n g Co ., B r o o -ma l l , PA.6 M o n o - a n d d i g ly c e r i d e s 8 0 % , P o l y s o r b a t e 8 0 2 0 % , G e r m a n t o w n M a n u f a c t u r i n g C o . , B r o o m a l l , P A .

c o n t a i n e r s a n d i n s ix . 9 4 - L c o n t a i n e r s . S a m p l e sw e r e p l a ce d i n t h e - 3 2 C h a r d e n i n g r o o mw h e r e t h e y r e m a i n e d f o r a m i n i m u m o f 4 8 hb e f o r e a n y t e s t i n g w a s d o n e . I c e c r e a m t r i a l sw e r e r e p l i c a te d o n f iv e d i f f e r e n t d a y s t o s e c u r ed a t a f o r s t a t i s t ic a l a n a l y s i s o f t h e v a r i a t i o nb e t w e e n t r ia l s ( r e p l i c a t i o n d a y s ) ,

MeasurementsG loss . T o e v a l u a t e t h e g l os s c h a r a c t e r i s t i c o f

t h e i c e c r e a m s a m p l e s , t h e f o u r e x p e r i e n c e d i cec r e a m m a k e r s w h o m a d e t h e ic e c r e a m t h r o u g h -o u t t h e e x p e r i m e n t g r a d ed a s a m p l e f r o m e a c ht r e a t m e n t . W h e n h a l f o f e a c h b a t c h w a s r u nt h r o u g h t h e f r e e z er , a l 1 3 - m l d i x ie c u p w a sf i ll e d w i t h i c e c r e a m . T h e i c e c r e a m w a s l e v e le di n t h e c u p b y s c r a p i n g a k i t c h e n s p a t u l a , h e l dp e r p e n d i c u l a r t o t h e i ce c r e a m s u r f a c e , a cr o s st h e t o p o f t h e c u p . T h e f o u r e x p e r i e n c e d i cec r e a m m a k e r s r a t e d t h e s a m p l e f o r it s g l os sc h a r a c t e r o n a s ca l e 0 to 5 . Z e r o r e p r e s e n t e d a ne x c e s s i v e l y d r y i c e c r e a m s a m p l e a n d 5 r e p r e -s e n t e d a v e r y g l o ss y , w e t i c e c r e a m s a m p l e . A l le v a l u a t i o n s w e r e m a d e a t t h e s a m e l o c a t i o n int h e p i l o t p l a n t s o t h a t l i g h t i n g d i f f e r en c e s w e r en o t a n i n f l u e n t i a l f a c t o r i n t h e g lo s s r at i n g s .

O v e r r u n . W h e n p a c k a g i n g t h e ic e c r e a m , t w o1 . 8 9 - L c o n t a i n e r s w e r e f i l l ed f i rs t a n d t h e n t h es i x .9 4 - L c o n t a i n e r s w e r e f il le d . T h e s e c o n d

1 . 8 9 - L c o n t a i n e r w a s u s e d t o m e a s u r e o v e r r u n .O v e r r u n w a s m e a s u r e d w i t h a P e l o u z e I c eC r e a m S c a le ( M o d e l Y 8 0 , B r a n s t o n , I L ) . T h es c a le w a s t a r e d f o r a p a p e r h a l f - g a l l o n c o n t a i n e r .T h e o v e r r u n m e a s u r e m e n t w a s r e ad a n d r e-c o r d e d .

S t i f f n e s s . S t i f f n e s s o f t h e ic e c r e a m w a sm e a s u r e d w i t h a r e c o r d in g a m m e t e r . T h ea m m e t e r w a s c o n n e c t e d i n s e ri es w i t h t h em o t o r t h a t t u r n e d t h e d a s h e r i n t h e fr e e z e rb a r r e l . S i n c e t h e s p e e d o f t h e f r e e z e r w a s k e p tc o n s t a n t t h r o u g h o u t t h e e x p e r i m e n t , t h ea m m e t e r m e a s u r e d t h e en e r g y n e ce s s a r y to t u r nt h e d a s h e r . T h e s t i f f e r th e i c e c re a m , t h e m o r ee n e r g y i s n e e d e d t o t u r n t h e d a s h e r to k e e p t h ef r e e z e r r u n n i n g a t a c o n s t a n t s p e ed . T h e m a x -i m u m p e a k o f t h e re c o r d e d a m p e r a g e u s e d f o re a c h h o m o g e n i z a t i o n t r e a t m e n t w a s u s e d a s t h es t i f f n e s s v a l u e.

F a t D e s t a b i l i z a t i o n . F a t d e s t a b i l i z a t i o n w a sm e a s u r e d a s d e s c r ib e d b y K e e n e y a n d J o s e p h -s o n ( 4 ). O n e g r a m o f i c e c r e a m m i x o r ic ec r e a m w a s w e i g h e d o u t . A 1 t o 5 0 0 - m l d i l u t i o nw a s m a d e w i t h d i s t i l le d w a t e r . F r o m t h isd i l u t i o n , 1 0 m l w a s c e n t r i f u g e d u s i n g th eI n t e r n a t i o n a l C e n t r i f u g e (M o d e l U V , I n t e r n a -t i o n a l E q u i p m e n t C o . , N e e d h a m , M A ) a t 1 0 0 0r p m f o r 5 m i n . T u b e s w e r e s e t f o r 1 0 m i n a tr o o m t e m p e r a t u r e w i t h o u t a g i t a t io n a n d t h e nm e a s u r e d f o r p e r c e n t a b s o r b a n c e o n a C o l e m a n

J o u r n a l o f D a i r y S c i e n c e V o l. 7 2 , N o . 2 , 1989

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HOMOGENIZATION PRESSURE EFFECTS ON ICE CREAM 381Junior II Spectrophotometer (Model 6/20)Coleman Instruments, Maywood, IL) at 540rim. Distilled water was used as the blank andwas set at 0 absorbance. Fat dest abilization wasmeasured by turbi dit y as: [(1 - absorbance ofthe ice cream)/absorba nce of the mix] x 100 =% fat destabilization. Duplicate samples weremade on both mix and ice cream samples.Values for the mix and ice cream were averagedseparately, then fat destabilization was cal-culated.Viscosity. Mixes were kept at 5C andmeasured for viscosity within 48 h after produc-tion. Viscosity was measured at 5C with aHaake Rotovisco II Viscometer (Haake-Buchler,Saddlebrook, NJ) fitted with a MVII sensorsystem and a size 50 head. A Haake 86Arefrigerated water bath was used to maintaintemperatures and a Hewlett Packard plotter(Model 1040A) was used to record viscosityreadings. Apparent viscosity was compared at ashear rate of 90 s - 1. Duplicates were run on allsamples and averaged.Microscopic Evaluation. All ice creams wereevaluated microscopically for fat globule sizeand dispersion. Ice creams were evaluatedwithin 72 h aft er production. A 1-g sample ofproduct was diluted with 4 g of 2C distilledwater. The mixture was mixed carefully with aglass stirring rod. A drop was placed on amicroscope slide, covered with a cover slip,and viewed u nder 400x magnific ation with aFisher Light Microscope (Micromaster ModelE Fisher Scientific, Pittsburgh, PA). Photo-graphs of three different fields of each slidewere taken. A Nikon F camera with Ko dak PlusX film was used for the photographs.Experimental Design

For overrun, stiffness, viscosity, and fatdestabilization, the experimen tal design was setup as a complete randomized block. The 10different homogenization samples were thetreat ments and the 5 d of replication were theblocks. In itially, ANOVA (SAS Insti tute , Cary,NC) was done on the raw data. Homogeniza-tion treatments with P>.05 were not analyzedfurther, and no differences among the treat-ments were reported. If the homogenizationtreatm ent P

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382 SCHM1DT AND SMIT H

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