Quality and Stability of Enzymically Peeled and Sectioned Citrus Fruit

Chapter 12

Quality and Stability of Enzymically Peeled and Sectioned Citrus Fruit

Downloaded by UNIV OF MONTANA on December 14, 2014 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch012

R. A. Baker and J. H. Bruemmer U.S. Citrus and Subtropical Products Laboratory, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 1909, Winter Haven, FL 33883-1909 Peeling and sectioning of citrus by vacuum infusion of pectinases resulted in cleaner sections with less adhering albedo and better quality than those from conventional machine-peeling followed by a lye bath. Enzyme separated segments were larger, waste was eliminated, and segments had adequate structure to allow marketing as a dry pack. When commercial pectinases were adjusted to equivalent peeling activity, segments differed in vesicle turgidity, membrane strength, and fluid loss during storage. Fluid loss from dry-pack segments was found to be correlated with loss of membrane strength. In stored, dry-pack unpasteurized grapefruit segments, naringin crystals formed in albedo cells still adhering to section membranes after treatment. Crystal formation was minimized by water sprays or lye solution dips. This process provides a new approach for commercial sectioning of citrus. As currently marketed, citrus sections (primarily grapefruit and orange) consist of segment juice sacs excised from the carpellary membranes. Before sections can be cut from fruit, a l l vestiges of inner peel or albedo must be removed. To accomplish this, present technology requires steaming the fruit to loosen the peel, machine peeling, and lye treatment of the peeled fruit to remove any remaining albedo. Section production is labor intensive in that each section must be cut by hand from the peeled fruit. Cut sections are small and friable, and because of damage incurred during cutting, must be packed in liquid. Only 60% of the edible portion of fruit is recovered as cut sections {V) . These inefficiencies have kept section costs high and driven much of the production capacity to cheaper labor markets. An alternate technology with the potential to minimize labor input and increase product yield was described by Bruemmer et a l . (_^, 2) . Vacuum infusion was utilized to permeate the albedo of grapefruit with any of several commercial pectinases. This chapter not subject to U.S. copyright Published 1989 American Chemical Society

In Quality Factors of Fruits and Vegetables; Jen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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Enzymically Peeled and Sectioned Citrus Fruit

D e p o l y m e r i z a t i o n o f m i d d l e l a m e l l a r p e c t i n s by t h e s e p r e p a r a t i o n s d i m i n i s h e d a l b e d o a n d s e g m e n t membrane i n t e g r i t y , f a c i l i t a t i n g p e e l removal and separation of s e c t i o n s . Sections thus produced, while l a r g e r a n d l e s s damaged t h a n c u t s e c t i o n s , s h a r e d t h e i r fragility. C o a t i n g w i t h g e l a t i n was s u g g e s t e d a s a means t o i n c r e a s e s t r u c t u r a l i n t e g r i t y o f enzyme s e p a r a t e d s e c t i o n s . R e c e n t work h a s shown t h a t s e c t i o n f i r m n e s s i s e n h a n c e d b y m o d i f y i n g t h e enzyme s e c t i o n i n g p r o c e s s t o l e a v e segment membranes i n t a c t (_3,4) . R e c o v e r y o f s e g m e n t s w i t h membrane c o v e r i n t a c t a l s o p e r m i t s u t i l i z a t i o n o f 100% o f t h e e d i b l e p o r t i o n o f f r u i t . Firm dry segments t h u s produced a r e amenable t o p a c k i n g w i t h o u t l i q u i d c o v e r , a s s u g g e s t e d b y Bruemmer e t a l (J_). U n p a s t e u r i z e d , d r y pack segments c o u l d p r o v i d e t h e consumer w i t h a p r o d u c t h a v i n g t h e q u a l i t y o f f r e s h f r u i t , i f f l a v o r , t e x t u r e , and m i c r o b i a l d e t e r i o r a t i o n c o u l d be controlled. The p u r p o s e o f t h i s s t u d y was t o o p t i m i z e i n i t i a l segment q u a l i t y a n d t o d e v e l o p means t o e x t e n d s h e l f l i f e o f d r y p a c k c i t r u s segments. M a t e r i a l s and Methods Vacuum I n f u s i o n . F r e s h washed g r a p e f r u i t ( C i t r u s p a r a d i s i Mac F . ) o r o r a n g e s ( C . s i n e n s i s L . ) w e r e w a r m e d t o 30°C c o r e t e m p e r a t u r e b y i m m e r s i o n i n warm w a t e r o r h o l d i n g o v e r n i g h t a t 32 C . To m i n i m i z e c o n t a m i n a t i o n o f segments by s u r f a c e m i c r o f l o r a , f r u i t were immersed i n b o i l i n g w a t e r f o r 90 s e c . F r u i t w e r e t h e n s c o r e d r a d i a l l y t h r e e times from stem t o blossom e n d , d i v i d i n g t h e p e e l i n t o s i x equal sections. This s c o r i n g , which penetrated the flavedo but not the albedo, f a c i l i t a t e d infusion of l i q u i d . A f t e r s c o r i n g , f r u i t were submerged i n a 30 C b a t h o f c o m m e r c i a l p e c t i n a s e i n d e i o n i z e d w a t e r , p l a c e d i n a vacuum chamber, a n d e v a c u a t e d t o a p p r o x i m a t e l y 75 torr. A f t e r h o l d i n g a t t h i s p r e s s u r e f o r t w o m i n u t e s , t h e vacuum was released slowly. I n f u s e d f r u i t w e r e s t o r e d f o r o n e h o u r a t 30 C before p e e l i n g and segmenting. E a s e o f p e e l r e m o v a l was e v a l u a t e d on a s c a l e o f 1 - 5 , w i t h one b e i n g s i m i l a r t o u n i n f u s e d f r u i t , and f i v e c o n n o t i n g e a s y , complete s l i p p a g e o f p e e l w i t h no a d h e r i n g t h r e a d s o r core. S e g m e n t i n g was s i m i l a r l y e v a l u a t e d , w i t h o n e e q u i v a l e n t t o u n t r e a t e d f r u i t , a n d f i v e i n d i c a t i n g t h a t segments s e p a r a t e d e a s i l y w i t h o u t c a r p e l l a r y membranes. I n i t i a l l y , p e c t i n a s e s were e v a l u a t e d f o r p e e l i n g a n d segmenting a c t i v i t y a t e q u i v a l e n t p r o t e i n l e v e l s , u s i n g t h e Lowry procedure as m o d i f i e d b y P o t t y (5) f o r p r o t e i n d e t e r m i n a t i o n . In l a t e r work, p e c t i n a s e s w e r e t e s t e d a t a number o f c o n c e n t r a t i o n s t o d e t e r m i n e t h e amount r e q u i r e d t o y i e l d a s p e c i f i c p e e l r a t i n g u s i n g r e g r e s s i o n analysis. Enzyme A c t i v i t y . Seven c o m m e r c i a l p e c t i n a s e s were o b t a i n e d from M i l e s L a b o r a t o r i e s , E l k h a r t , IN 46514, Novo L a b o r a t o r i e s , W i l t o n , CN 0 6 8 9 7 , a n d Rohm T e c h I n c . , M a i d e n , MA 0 2 1 4 8 . A l l preparations were assayed f o r p o l y g a l a c t u r o n a s e ( P G ) , c e l l u l a s e , and p e c t i n e s t e r a s e ( P E ) a c t i v i t i e s b y t h e m e t h o d s o f V a s , e t a l . (6^) a s m o d i f i e d b y B r u e m m e r e t a l . (J_) . PG a n d c e l l u l a s e a c t i v i t i e s w e r e determined by r e d u c t i o n of s p e c i f i c v i s c o s i t y i n an Ostwald-type v i s c o s i m e t e r h e l d i n a 50 C w a t e r b a t h . PG a c t i v i t y was m e a s u r e d on b o t h 1.5% p o l y g a l a c t u r o n i c a c i d ( U . S . B i o c h e m i c a l C o r p . ) , titrated


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t o p H 5 . 0 w i t h N a OH , a n d o n 0 . 4 5 % r a p i d - s e t l e m o n p e c t i n ( S u n k i s t Growers, I n c . ) . C a r b o x y m e t h y l c e l l u l o s e (2%) was u s e d a s t h e substrate for cellulase a c t i v i t y . D e c r e a s e i n s p e c i f i c a c t i v i t y was graphed a g a i n s t the l o g of i n o c u l a t i o n t i m e , and the time r e q u i r e d f o r 25% r e d u c t i o n o f i n i t i a l v i s c o s i t y d e t e r m i n e d . A u n i t of a c t i v i t y was d e f i n e d a s t h e amount o f enzyme n e c e s s a r y t o e f f e c t a 25% r e d u c t i o n i n i n i t i a l v i s c o s i t y o f 6 m l o f s u b s t r a t e i n 10 m i n . P E a c t i v i t y was d e t e r m i n e d w i t h 15 m l o f 1% p e c t i n s o l u t i o n a d j u s t e d t o pH 4 . 0 p r i o r t o a d d i t i o n o f e n z y m e . C o n s u m p t i o n o f 0 . 1 Ν NaOH a t 50 C w a s g r a p h e d , t h e s l o p e d e t e r m i n e d b y l e a s t s q u a r e s , a n d P E u n i t s c a l c u l a t e d b y t h e p r o c e d u r e o f R o u s e (_7 ) . Microbial Stability. E n z y m i c a l l y p e e l e d and segmented g r a p e f r u i t were u s e d t o d e t e r m i n e s u s c e p t i b i l i t y of u n p a s t e u r i z e d segments t o microbial colonization. A l t h o u g h r e a s o n a b l e s a n i t a r y p r o c e d u r e s were f o l l o w e d d u r i n g s e g m e n t p r e p a r a t i o n , n o a t t e m p t w a s made t o m a i n t a i n an a s e p t i c e n v i r o n m e n t ; segments were t h e r e f o r e presumed t o have an endogenous m i c r o f l o r a . Segments were s e a l e d i n p o l y e t h y l e n e bags w i t h and w i t h o u t p r i o r d i p p i n g i n 0.2% potassium s o r b a t e , and s t o r e d a t 2 C. A s i m i l a r g r o u p o f s e g m e n t s was c h a l l e n g e d w i t h a n i n o c u l a t i o n o f common c i t r u s f r u i t d e c a y m i c r o o r g a n i s m s b e f o r e b e i n g bagged w i t h o r w i t h o u t t h e s o r b a t e d i g s . Inoculum contained the yeast S a c c h a r o m y c e s c e r e v i s i a e a t 10 c o l o n y f o r m i n g u n i t s (CFU) per g of t i s s u e and t h e b a c t e r i a L a c t o b a c i l l u s p l a n t a r u m ang L e u c o n o s t o c m e s e n t e r o i d e s a t l e v e l s p r o v i d i n g a t o t a l o f 10 CFU's/g of f r u i t . At weekly i n t e r v a l s bags were withdrawn from s t o r a g e ; five segments o f each t r e a t m e n t were w e i g h e d , combined w i t h t w i c e t h e i r v o l u m e o f 0 . 1 % p e p t o n e , a n d b l e n d e d a t h i g h s p e e d f o r 10 s e c . After d i l u t i o n , samples were p l a t e d i n d u p l i c a t e on a c i d i f i e d p o t a t o d e x t r o s e a g a r (PDA) f o r e n u m e r a t i o n o f y e a s t s a n d o r a n g e s e r u m a g a r (OSA) f o r d e t e c t i o n o f b a c t e r i a . P l a t e s w e r e i n c u b a t e d f o r 72 h r a t 25°C (PDA) o r 35°C (OSA) b e f o r e r e a d i n g . F l u i d Loss and T e x t u r e . L i q u i d l o s s from dry pack segments d u r i n g 2 C s t o r a g e was m e a s u r e d b y w e i g h i n g s e g m e n t s i n a r e c l o s a b l e b a g , d r a i n i n g f r e e l i q u i d from the bag weekly, and r e w e i g h i n g . L o s s was expressed as % of o r i g i n a l weight. Two a s p e c t s o f t e x t u r e w e r e c o n s i d e r e d : f i r m n e s s o f t h e i n t a c t segment and t o u g h n e s s o f t h e c a r p e l l a r y membrane. B o t h were measured o n s t o r e d s e g m e n t s w i t h a n I n s t r o n m o d e l 1011 U n i v e r s a l T e s t e r ( I n s t r o n C o r p . , C a n t o n MA 0 2 0 2 1 ) s e t o n c o m p r e s s i o n m o d e . Firmness was d e t e r m i n e d b y c r u s h i n g a p a i r o f s e g m e n t s i n a n O t t o w a T e x t u r e M e a s u r e m e n t S y s t e m t o 3 mm f i n a l t h i c k n e s s . Crushed segments were then t r a n s f e r r e d t o a Kramer Shear C e l l and t h e f o r c e n e c e s s a r y t o s h e a r t h e membranes d e t e r m i n e d . Flavor Comparisons. R e l a t i v e f l a v o r q u a l i t y o f segments s t o r e d i n s e a l e d p l a s t i c b a g s o f v a r y i n g o x y g e n p e r m e a b i l i t i e s was m e a s u r e d w i t h a r a n k sum t e s t (8). F r e s h segments were bagged i n h i g h l y permeable s t r i p s e a l e d p o l y e t h y l e n e bags, composite heat s e a l e d bags of i n t e r m e d i a t e 0 p e r m e a b i l i t y (3000 cc/m d a y ) , and heat s e a l e d b a g s o f l o w O^ p e r m e a b i l i t y ( 4 - 6 c c / m d a y ) . Bags were s t o r e d a t 2 C and sampled a t weekly i n t e r v a l s . To e l i m i n a t e s e g m e n t v a r i a b i l i t y , 24 s e g m e n t s f r o m e a c h s t o r a g e r e g i m e w e r e b l e n d e d f o r 10 2

2


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sec, f i l t e r e d through cheesecloth, and tested as the j u i c e . An e x p e r i e n c e d p a n e l o f 20 j u d g e s w a s p r e s e n t e d t h e j u i c e s i n r e d g l a s s e s i n a r e d i l l u m i n a t e d p o s i t i v e p r e s s u r e room, and asked t o r a n k t h e m i n o r d e r o f p r e f e r e n c e . R a n k sums w e r e c o m p u t e d a n d s i g n i f i c a n c e o f r e s u l t s d e t e r m i n e d f r o m t a b l e s (9^). Calcium Firming. S o f t segments from l a t e season f r u i t were c o a t e d w i t h an e d i b l e c a l c i u m a l g i n a t e f i l m t o improve f i r m n e s s . Segments were d i p p e d i n a l g i n a t e s o l u t i o n , d r a i n e d b r i e f l y , t h e n immersed i n C a C l hardener s o l u t i o n . A d d i t i o n a l c a l c i u m w a s p r o v i d e d f o r some s e g m e n t s b y s u p p l e m e n t a t i o n o f t h e h a r d e n e r s o l u t i o n w i t h 5% C a a s CaCl . 2


2

Surface Naringin Reduction. C r y s t a l aggregates o c c u r r i n g on surfaces of s t o r e d segments were c o l l e c t e d , p u r i f i e d by r e c r y s t a l l i z a t i o n and TLC, a n d c o n f i r m e d a s n a r i n g i n by m e l t i n g p o i n t , I R , a n d TLC i n s e v e r a l s o l v e n t s y s t e m s ( B a k e r , R. Α . , a n d P a r i s h , M . E . , J o u r . F o o d Sci., i n press). R e d u c t i o n o f s u r f a c e n a r i n g i n l e v e l s was a t t e m g t e d w i t h w a t e r m i s t s p r a y a n d b y a 10 s e c i m m e r s i o n i n 1% NaOH a t 6 0 C , f o l l o w e d by water m i s t i n g . R e s i d u a l s u r f a c e n a r i n g i n was removed f o r a n a l y s i s by g e n t l y s c r u b b i n g t h e segment s u r f a c e w i t h a s o f t b r u s h w h i l e immersed i n d e i o n i z e d w a t e r . N a r i n g i n c o n t e n t s o f wash w a t e r s a n d b l e n d e d s e g m e n t s w e r e d e t e r m i n e d b y t h e D a v i s t e s t (_10^) . Results and Discussion Enzyme A c t i v i t y a n d P e e l i n g E f f i c a c y . Excessive treatment with i n f u s e d p e c t i n a s e s c a u s e d segment membranes t o s e p a r a t e f r o m j u i c e sacs, y i e l d i n g s o f t , f r i a b l e segments. T e r m i n a t i o n o f a c t i v i t y when a p e e l i n g a n d s e c t i o n i n g r a t i n g o f 4 was a c h i e v e d i m p r o v e d segment t e x t u r a l q u a l i t y by r e t a i n i n g c a r p e l l a r y membranes. Ease o f p e e l i n g was s t i l l a c c e p t a b l e a t t h i s a c t i v i t y l e v e l . Peeling and s e c t i o n i n g ratings of grapefruit infused with commercial pectinases a t equivalent p r o t e i n l e v e l s v a r i e d from 2 . 5 t o 4.0 (Table I ) . Table

I.

E f f e c t o f P e c t i n a s e s I n f u s e d a t, E q u i v a l e n t L e v e l s o n P e e l i n g , S e c t i o n i n g , and Segment F l u i d Loss Section Fluid Peel Pectinase Rating Rating Loss % 1 3.0 2.5 2.9 2 3.0 2.5 3.0 3 4.0 4.0 4.3 4 3.8 3.8 8.2 5 9.4 3.4 3.8 6 4.0 11.3 2.8 7 3.0 13.0 3.0 Cut S e c t i o n s 16.1

-

While t h e two p e c t i n a s e s w i t h t h e b e s t p e e l i n g and s e c t i o n i n g r a t i n g s d i d h a v e t h e h i g h e s t PG a c t i v i t y p e r u n i t p r o t e i n , o t h e r p e c t i n a s e s s h o w e d n o c o r r e l a t i o n b e t w e e n r a t i n g s a n d PG a c t i v i t y ( £ ) . PE and c e l l u l a s e a c t i v i t y l e v e l s were u n r e l a t e d t o p e e l i n g o r s e c t i o n i n g a b i l i t y , a s was n o t e d b y Bruemmer ( 1 ) . F l u i d l o s s was n o t c o r r e l a t e d


143

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t o p e e l i n g or s e c t i o n i n g e f f i c a c y of p e c t i n a s e s , nor t o t h e i r s p e c i f i c enzyme a c t i v i t i e s . At concentrations p r o v i d i n g equivalent p e e l i n g r a t i n g s , p e c t i n a s e s should e x h i b i t s i m i l a r a c t i v i t y l e v e l s of the r e s p o n s i b l e enzyme(s). H o w e v e r , when t h e c o n c e n t r a t i o n s n e c e s s a r y f o r a 4 p e e l r a t i n g were d e t e r m i n e d f o r each p e c t i n a s e s by r e g r e s s i o n a n a l y s i s , a n d t h e i n d i v i d u a l enzyme a c t i v i t i e s c a l c u l a t e d f o r t h o s e c o n c e n t r a t i o n s , n o s u c h s i m i l a r i t y was e v i d e n t ( T a b l e II.) Enzyme A c t i v i t i e s o f P e c t i n a s e I n f u s i o n s G i v i n g a P e e l R a t i n g of 4 PG PG Cellulase pectin PGA PEU 37 94 100 10 85 177 11 273 214 115 1619 24 118 17 581 27 343 41 18 21 9 17 18 26 11 269 10


Table II.

Pectinase 1 2 3 4 5 6 7

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A c t i v i t y ranges were 9 - f o l d f o r c e l l u l a s e , 2 7 - f o l d f o r PE, and 1 6 0 - f o l d f o r PG. Several f a c t o r s could account f o r t h i s lack of correspondence. Pure substrates are used i n assays, while mixed substrates are encountered w i t h i n the p e e l . The p e c t i n a s e s a r e c r u d e e x t r a c t s c o n t a i n i n g many m o r e a c t i v i t i e s t h a n t h o s e a s s a y e d , e . g . , pectin lyase. To o b t a i n a m o r e a c c u r a t e e s t i m a t e o f a p e c t i n a s e s p e e l i n g a b i l i t y , B e n - S h a l o m e t a l . (VV) s u g g e s t e d u s i n g a s u b s t r a t e derived from a l c o h o l i n s o l u b l e s o l i d s of c i t r u s p e e l . In a d d i t i o n , p e c t i n a s e s v a r i e d c o n s i d e r a b l y i n pH a n d t e m p e r a t u r e o p t i m a a n d stability. F o r some p e c t i n a s e s , a s s a y e d a c t i v i t i e s may b e s u b s t a n t i a l l y greater than a c t i v i t i e s seen i n p e e l . An a s s a y i n c o r p o r a t i n g s u b s t r a t e s and c o n d i t i o n s s i m i l a r t o those found i n p e e l may b e u s e f u l i n s c r e e n i n g f o r p e e l i n g a c t i v i t y , b u t s t a n d a r d a s s a y s a p p e a r t o be o f l i m i t e d v a l u e a s p r e d i c t o r s . 1

Textured P r o p e r t i e s of Stored Segments. When g r a p e f r u i t w e r e and segmented w i t h p e c t i n a s e s a t c o n c e n t r a t i o n s y i e l d i n g p e e l o f 4 , f l u i d l o s s f r o m s e g m e n t s d u r i n g 2°C s t o r a g e v a r i e d f r o m t o 28% ( T a b l e III). Table Pectinase Water Con 1 6 4 7 5 3 2

peeled ratings 9.4

III. T e x t u r a l P r o p e r t i e s o f S t o r e d Segments Liquid Membrane Vesicle Loss % Comp. (lbs) Shear (lbs) 4.0 242.0 239.0 9.4 151.3 164.9 13.1 108.8 98.7 14.5 90.9 107.1 15.9 88.5 120.5 16.7 106.7 121.9 24.1 73.0 96.9 28.0 92.5 82.9



12.

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T h i s c o m p a r e d t o a 4% f l u i d l o s s f r o m s e g m e n t s d e r i v e d f r o m w a t e r infused control f r u i t . F l u i d l o s s l e v e l s were h i g h e r t h a n i n Table I due t o t h e u s e o f s o f t e r , l a t e s e a s o n f r u i t i n t h i s e x p e r i m e n t . F i r m n e s s o f segments was s u b s t a n t i a l l y r e d u c e d b y t h e p e c t i n a s e infusion process. V e s i c l e compression values f o r pectinase derived s e g m e n t s r a n g e d f r o m 3 8 t o 69% o f t h e v a l u e f o r w a t e r i n f u s e d c o n t r o l segments. Of t h e p e c t i n a s e d e r i v e d s e g m e n t s , t h o s e p r o d u c e d w i t h P e c t i n a s e 1 were t h e f i r m e s t , and a l s o h a d t h e l e a s t f l u i d l o s s during storage. S e g m e n t t o u g h n e s s , a s m e a s u r e d b y membrane s h e a r , w a s a l s o reduced by p e c t i n a s e t r e a t m e n t . Some r e d u c t i o n o f membrane t o u g h n e s s i s d e s i r a b l e i f segments ( p a r t i c u l a r l y t h o s e o f g r a p e f u r i t ) a r e p r o d u c e d w i t h c a r p e l l a r y membranes i n t a c t . Shear v a l u e s of t r e a t e d s e g m e n t s v a r i e d f r o m 30 t o 65% o f c o n t r o l s e g m e n t s h e a r , w i t h Pectinase 1 again giving the highest value. I n g e n e r a l , membrane s h e a r was c o m p a r a b l e t o v e s i c l e c o m p r e s s i o n f o r p e c t i n a s e s , w i t h P e c t i n a s e 1 y i e l d i n g segments w i t h h i g h e s t v a l u e s , and P e c t i n a s e s 2 and 3 , t h e l o w e s t . An i n v e r s e c o r r e l a t i o n between f i r m n e s s a n d f l u i d l o s s was s e e n w i t h P e c t i n a s e s 1 , 2 , a n d 3 , b u t n o t t h e o t h e r pectinases. Microbial Stability. B a c t e r i a l contamination of uninoculated s e g m e n t s w a s l o w , a n d d e c l i n e d d u r i n g 9 w e e k s o f 2°C s t o r a g e ( T a b l e IV). Table

Week 0 1 3 5 7 9 0 1 3 5 7 9

IV.

B a c t e r i a l and Y e a s t Growth i n S t o r e d Segments U n i n o c u l a t e d Segments L o g CFU/g T i s s u e Bacteria Yeast Control Control + Sorbate + Sorbate 1.5 0.5 0.5 1.5 0.6 0.5 1.2 0.8 0.5 0.5 0.5 0.5 0.8 0.5 0.5 1.8 0.5 3.4 0.5 0.5 0.5 0.5 0.5 6.1 I n o c u l a t e d Segments 6.2 4.2 6.2 4.2 6.0 4.0 4.0 6.3 6.0 4.4 3.7 5.8 6.2 4.7 4.2 6.0 6.0 3.8 5.6 4.8 6.4 5.6 5.3 3.9

D i p p i n g segments i n 0.2% p o t a s s i u m s o r b a t e b e f o r e s t o r a g e d i d n o t accelerate this decline. Y e a s t c o n t a m i n a t i o n o f d r y p a c k e d segments was a l s o l o w i n i t i a l l y , b u t b e g a n t o i n c r e a s e r a p i g l y a f t e r t h r e e weeks o f s t o r a g e . T h i s i n c r e a s e , w h i c h r e a c h e d 10 C F U / g a f t e r 9 w e e k s , was c o m p l e t e l y s u p p r e s s e d b y t h e 0 . 2 % s o r b a t e d i p . Initia^ b a c t e r i a l l e v e l s o f i n o c u l a t e d s e g m e n t s a v e r a g e d s l i g h t l y o v e r 10 CFU/g. T h e r e was no i n c r e a s e i n CFU d u r i n g s t o r a g e ; a p p a r e n t l y t h e c o m b i n a t i o n o f l o w t e m p e r a t u r e a n d l o w segment pH i n h i b i t e d g r o w t h o f the added L a c t o b a c i l l u s and L e u c o n o s t o c . A s l i g h t reduction i n CFU s was s e e n when i n o c u l a t e d s e g m e n t s w e r e t r e a t e d w i t h s o r b a t e . Initial Saccharomyces c e r e v i s i a e l e v e l s i n i n o c u l a t e d segments averaged 1


145

146


s l i g h t l y above 10** C F U / g , a n d i n c r e a s e d t o 1 0 C F U / g d u r i n g storage. No g r o w t h o f y e a s t o c c u r r e d when s e g m e n t s w e r e t r e a t e d w i t h sorbate. These r e s u l t s s u g g e s t t h a t , i f s t o r e d a t 2 C, segments would n o t be s u b j e c t t o a p p r e c i a b l e b a c t e r i a l g r o w t h . Yeast growth does o c c u r u n d e r t h e s e c o n d i t i o n s , b u t c a n be c o n t r o l l e d w i t h potassium sorbate. I t was a l s o f o u n d t h a t g r o w t h o f y e a s t was suppressed by 2 C s t o r a g e i n b a g s o f l o w permeability.


J

Flavor S t a b i l i t y . Enzyme p e e l e d u n p a s t e u r i z e d s e g m e n t s a r e v i a b l e t i s s u e , and are thus s u b j e c t t o both enzymic and nonenzymic f l a v o r degradation. A n a t t e m p t w a s made t o c o n t r o l f l a v o r d e t e r i o r a t i o n b y p a c k a g i n g f r e s h l y p r e p a r e d segments i n s e a l e d p l a s t i c bags of l i m i t e d oxygen p e r m e a b i l i t y . F l a v o r of segments s t o r e d a t 2 C i n h i g h l y permeable p o l y e t h y l e n e bags d e t e r i o r a t e d r a p i d l y , and a f t e r t h r e e w e e k s w a s d i s l i k e d b y a n e x p e r i e n c e d t a s t e p a n e l a t t h e 1% l e v e l o f s i g n i f i c a n c e (Table V). Table

V.

R a n k Sums o f S e g m e n t s S t o r e d i n B a g s of Varying 0 ^ P e r m e a b i l i t y 0 Permeability High Medium Low 52 49 43 55 41 48 63 38 43 i n s i g n i f i c a n c e : 5 % , 4 0 - 5 6 ; 1%; 3 7 - 5 9 2

Week 1 2 3 Ranges o f

The p a n e l f o u n d n o s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e s e g m e n t s i n medium a n d l o w p e r m e a b i l i t y bags a f t e r two weeks s t o r a g e , b u t a f t e r t h r e e w e e k s s t o r a g e p r e f e r r e d ( a t 5% l e v e l o f s i g n i f i c a n c e ) s e g m e n t s stored i n moderately permeable bags. A r e s t r i c t e d (but not a n a e r o b i c ) o x y g e n e n v i r o n m e n t w o u l d seem t o be e s s e n t i a l f o r f l a v o r s t a b i l i t y of dry packed unpasteurized segments. Calcium Firming. C i t r u s s e c t i o n s t e n d t o become p r o g r e s s i v e l y softer as f r u i t mature, s e v e r e l y l i m i t i n g the p e r i o d i n which f i r m , h i g h q u a l i t y s e c t i o n s can be p r o d u c e d . A t t e m p t s h a v e b e e n made t o e x t e n d t h e p r o d u c t i o n s e a s o n by f i r m i n g canned s e c t i o n s w i t h c a l c i u m s a l t s added t o t h e p a c k i n g s y r u p ( 1 2 ) . W i t h dry pack segments a n o t h e r means m u s t b e f o u n d t o a p p l y c a l c i u m s a l t s . P r e l i m i n a r y work r e v e a l e d t h a t simultaneous i n f u s i o n of c a l c i u m l a c t a t e and p e c t i n a s e s f o r p e e l i n g was u n s u c c e s s f u l . At l e v e l s adequate t o f i r m segments, c a l c i u m i n t e r f e r e d w i t h p e c t i n a s e p e e l i n g and segment s e p a r a t i o n . A secondary i n f u s i o n of f r u i t w i t h calcium l a c t a t e or c h l o r i d e a f t e r p e e l i n g was a l s o u n s u c c e s s f u l , a s was d i p p i n g i n c a l c i u m s a l t solutions. C o a t i n g segments w i t h an e d i b l e a l g i n a t e f i l m u t i l i z i n g a calcium s a l t hardener provided s u f f i c i e n t calcium to e f f e c t i v e l y f i r m s o f t , l a t e season segments (Table V I ) . C a l c i u m s u p p l i e d by t h e h a r d e n e r i n c r e a s e d s e g m e n t f i r m n e s s 5 4 % , a n d membrane s h e a r , 50% o v e r controls. A n a d d i t i o n a l 5% c a l c i u m i n t h e h a r d e n e r f u r t h e r i n c r e a s e d s e g m e n t f i r m n e s s a n d membrane s h e a r o v e r c o n t r o l v a l u e s , b y 89 a n d 85%, r e s p e c t i v e l y .


12.

BAKER & BRUEMMER

Texture and F l u i d Loss of Uncoated and A l g i n a t e C o a t e d S e g m e n t s A f t e r 5 Weeks S t o r a g e Fluid Membrane Vesicle Loss % Shear ( l b s ) Comp. ( l b s ) Treatment 24.1 102.1 Uncoated 77.4 22.6 152.8 Alginate 119.3 20.3 189.0 A l g . + 5% C a 142.8


Table


VI.

R e d u c t i o n o f f l u i d l o s s from s t o r e d segments by c a l c i u m c o a t i n g was n o t c o m m e n s u r a t e w i t h i n c r e a s e d s e g m e n t f i r m n e s s o r membrane toughness. F o r e x a m p l e , a n 89% i n c r e a s e i n f i r m n e s s w a s a c c o m p a n i e d b y o n l y a 16% d e c r e a s e i n l o s t l i q u i d s . I n c r e a s i n g f i r m n e s s due t o c a l c i u m c r o s s - l i n k i n g o f s t r u c t u r a l p e c t i n s was i n s u f f i c i e n t t o b l o c k migration and l o s s of j u i c e v e s i c l e f l u i d s . Naringin Crystallization. G r a p e f r u i t s e g m e n t s s t o r e d a t 2°C o f t e n developed s m a l l white specks, predominently on t h e outer (peel contact) surface. Microscopic examination of these specks revealed t h e y were s t e l l a t e o r f a n - s h a p e d c l u s t e r s o f c o l o r l e s s n e e d l e shaped crystals. When p u r i f i e d b y T L C a n d r e c r y s t a l l i z e d , t h e i r m e l t i n g p o i n t , I R , a n d TLC b e h a v i o r i d e n t i f i e d t h e s e a s n a r i n g i n ( B a k e r , R. Α . , a n d P a r i s h , M . E . , J o u r . F o o d S c i . , i n p r e s s ) . In addition t o b e i n g a v i s u a l d e f e c t , t h e i n t e n s e b i t t e r n e s s o f n a r i n g i n made t h e presence of these c r y s t a l s undesirable. When t h e o u t e r s u r f a c e o f enzyme p e e l e d s e g m e n t s was e x a m i n e d , a t h i n l a y e r o f a d h e r i n g a l b e d o c e l l s was f o u n d . G r a p e f r u i t albedo contains from 2-5% n a r i n g i n ( 1 3 ) ; c r y s t a l l i z a t i o n during storage of the sections occurred within t h i s layer of infused albedo c e l l s . S i n c e most n a r i n g i n o f g r a p e f r u i t o c c u r s i n t h e a l b e d o a n d segment membranes, a n d t h e s e a r e removed i n c o n v e n t i o n a l p r o c e s s i n g , c r y s t a l l i z a t i o n of n a r i n g i n has n o t been reported as a problem i n cut s e c t i o n s . I n e n z y m e p e e l e d s e g m e n t s , a p p r o x i m a t e l y 18% o f t h e t o t a l n a r i n g i n was l o c a l i z e d i n t h e l a y e r o f a l b e d o c e l l s o n t h e o u t e r membrane. A t t e m p t s t o remove t h e s e c e l l s p r i o r t o s t o r a g e b y w a t e r m i s t i n g o f w h o l e p e e l e d f r u i t r e d u c e d s u r f a c e n a r i n g i n t o 12% o f t h e segment t o t a l . S u r f a c e n a r i n g i n c o u l d b e r e d u c e d t o 9% o f t h e s e g m e n t t o t a l b y a b r i e f i m m e r s i o n o f w h o l e p e e l e d f r u i t i n 1% N a O H , f o l l o w e d by water m i s t i n g . Gentle b r u s h i n g o f whole p e e l e d f r u i t under a water spray o r h o t water m i s t i n g c o u l d be o t h e r a l t e r n a t i v e s for reducing surface naringin levels. Segments p r o d u c e d w i t h different pectinases varied i n s u s c e p t i b i l i t y t o specking, suggesting the presence of naringinase a c t i v i t y i n c e r t a i n pectinases ( 1 4 ) . I n f u s i o n w i t h naringinase a c t i v e pectinases could reduce surface c r y s t a l l i z a t i o n of naringin without further treatment. A s i m i l a r surface c r y s t a l l i z a t i o n of glucoside occurs i n freeze d a m a g e d o r a n g e s , when h e s p e r i d i n s p e c k s a p p e a r o n c a r p e l l a r y membranes ( 1 5 ) . I n l i m i t e d work w i t h p e c t i n a s e p e e l e d o r a n g e s , n o c r y s t a l l i z a t i o n o f h e s p e r i d i n o c c u r r e d i n segments d u r i n g s t o r a g e . Conclusions. Pectinase p e e l i n g and segmenting of c i t r u s f r u i t o f f e r s a n a l t e r n a t i v e m e t h o d o l o g y t o c u r r e n t t e c h n i q u e s , a n d may substantially increase y i e l d . M a r k e t i n g o f segments a s a d r y p a c k e d r e f r i g e r a t e d product requires that t e x t u r a l , m i c r o b i a l , and f l a v o r d e t e r i o r a t i o n s be c o n t r o l l e d . F l u i d l o s s and firmness of stored

American Chemical Society Library 1155 16th St.,Vegetables; N.W. Jen, J.; In Quality Factors of Fruits and ACS Symposium Series;Washington. American Chemical Washington, DC, 1989. D.C.Society: 20036

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segments v a r i e d w i t h p e c t i n a s e used a n d m a t u r i t y o f f r u i t . Coating s o f t segments from l a t e season f r u i t w i t h a c a l c i u m a l g i n a t e f i l m w i t h o r w i t h o u t a n a d d i t i o n a l 5% C a i n t h e h a r d e n e r i n c r e a s e d f i r m n e s s , and t o a l e s s e r degree decreased f l u i d l o s s . Segments s t o r e d a t 2 C i n c u r r e d l i t t l e b a c t e r i a l growth, b u t were s u b j e c t t o contamination with yeast. Y e a s t growth c o u l d be p r e v e n t e d e i t h e r by d i p p i n g s e g m e n t s i n 0.2% p o t a s s i u m s o r b a t e o r b y s e a l i n g i n b a g s o f low oxygen p e r m e a b i l i t y . F l a v o r q u a l i t y o f c h i l l e d segments d e t e r i o r a t e d r a p i d l y i n h i g h l y permeable packaging; r e s t r i c t e d atmosphere bagging r e t a r d e d f l a v o r changes. Both f l a v o r and appearance were a d v e r s e l y a f f e c t e d by n a r i n g i n c r y s t a l l i z a t i o n o n segment s u r f a c e s d u r i n g s t o r a g e . Surface n a r i n g i n l e v e l s c o u l d be r e d u c e d b y w a t e r m i s t i n g , w a s h i n g w i t h 1% N a O H , o r p o s s i b l y b y u s i n g pectinases containing naringinase a c t i v i t y .

Literature Cited. 1. Bruemmer, J . H . ; Griffin, A.W.; Onayemi, O. Proc. F la. State Hort. Soc. 1978, 91, 112-114. 2. Bruemmer, J . H . U.S. Patent 4284651. 1981. 3. Baker, R.A. Proc. 1987 Subtrop. Tech. Conf., 197, p. 14. 4. Baker, R.A.; Foerster, J . A . ; Parish, M.E. Proc. 1988 Subtrop. Tech. Conf. 1988. 5. Potty, V.H. Anal. Biochem. 1969, 29, 535-539. 6. Vas, Κ; Nedbalek, M.; Scheffer, H.; Kovacs-Proszt, G. Fruch.-Ind. 1967, 12, 164-184. 7. Rouse, A . H . ; Atkins, C.D. Technical Bull. No. 570, U. of Fla., 1955. 8. Kramer, A. Food Tech. 1960, 14, 576-581. 9. Kramer, A. Food Tech. 1963, 17, 124-125. 10. Davis, W.B. Anal. Chem. 1947, 19, 476-478. 11. Ben-Shalom, Ν.; Levi, Α.; Pinto, R. Jour. Food Sci. 1986, 51, 421-423. 12. Olsen, R.W.; Barron, R.W.; Huggart, R . L . ; Wenzel, F.W. Proc. Fla. State Hort. Soc. 1966, 79, 326-330. 13. Sinclair, W. B. The Grapefruit, Its Composition Physiology, and Products; Univ. C a l i f . : Riverside, 1972. 14. Roe, B.; Bruemmer, J. H. Proc. F l a . State Hort. Soc. 1976, 89, 191-194. 15.

Hume, H.H. Citrus Fruits; MacMillan, New York, 1957, p. 292.

RECEIVED March 27, 1989


Quality and Stability of Enzymically Peeled and Sectioned Citrus Fruit

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