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Downloaded by UNIV OF MASSACHUSETTS AMHERST on February 11, 2016 | http://pubs.acs.org Publication Date: December 15, 1980 | doi: 10.1021/bk-1980-0143.ch002
Studies on the Role of Citrus in Health and Disease M. MANSOOR BAIG and JAMES J. CERDA Department of Medicine, Division of Digestive Disease and Nutrition, J-214 JHMHC, University of Florida College of Medicine, Gainesville, FL 32610
Since 1973, we at the University of Florida have been systematically evaluating the role of citrus fruits and their products in human n u t r i t i o n . Our previous studies of citrus have yielded valuable information relating to the beneficial nutritional role of citrus in providing certain vitamins, replenishing lost elect r o l y t e s , and possibly i n h i b i t i n g v i r a l infections. Our ongoing research in the area of study of the chemistry and biological role of dietary citrus pectin i n human nutrition has yielded results elucidating the complex chemical nature of pectin and the possible biochemical basis by which dietary pectin may cause lowering of serum and/or l i v e r cholesterol. In addition, another series of ongoing experiments suggest that citrus pectin may influence the biological processes regulating the absorption of glucose i n patients with postprandial hypoglycemia. This a r t i c l e i s a review of our major biomedical research efforts, previous and ongoing, on the role of citrus and citrus pectin i n human n u t r i t i o n . Its purpose i s to focus attention, provide s c i e n t i f i c evidence and evaluate the direction of future research on the beneficial role of citrus fruits in human nutrition. NUTRITIONAL ROLE OF CITRUS BEVERAGES B i o a v a i l a b i l i t y o f Water-soluble Vitamins N u t r i t i o n a l l y , the most important w a t e r - s o l u b l e vitamins i n c i t r u s f r u i t s are a s c o r b i c a c i d , f o l i c a c i d and p y r i d o x i n e . C l i n i cal s t u d i e s on the b i o a v a i l a b i l i t y o f these v i t a m i n s , as w e l l as basic research on the absorption and chemistry o f these v i t a m i n s , have y i e l d e d v a l u a b l e information adding to our o v e r a l l understanding o f the n u t r i t i o n a l q u a l i t y and b i o a v a i l a b i l i t y o f these vitamins found i n c i t r u s f r u i t s . Ascorbic A c i d .
U n l i k e a number o f animal s p e c i e s , man and
0-8412-05 95-7/80/47-143-025$05.00/0 © 1980 American Chemical Society In Citrus Nutrition and Quality; Nagy, Steven, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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CITRUS NUTRITION AND QUALITY
other primates as well as the guinea p i g depend on d i e t a r y sources f o r t h e i r v i t a m i n C needs because these species l a c k the b i o chemical mechanism to s y n t h e s i z e t h i s e s s e n t i a l n u t r i e n t . Lack of v i t a m i n C i n d i e t a r y sources causes scurvy i n a d u l t s which i s c h a r a c t e r i z e d by sore spongy gums, impaired c a p i l l a r y i n t e g r i t y w i t h subcutaneous hemorrhages and edema, j o i n t p a i n , anorexia and anemia. In c h i l d r e n , v i t a m i n C d e f i c i e n c y causes tenderness and s w e l l i n g of j o i n t s , a r r e s t e d s k e l e t a l development, impaired wound h e a l i n g , anemia and inadequate tooth development. C i t r u s j u i c e i s r i c h i n a s c o r b i c a c i d and, t h e r e f o r e , i s an important d i e t a r y source of t h i s e s s e n t i a l v i t a m i n . Our s t u d i e s were aimed a t d e f i n i n g whether v i t a m i n C from c i t r u s sources i s comparable w i t h the s y n t h e t i c v i t a m i n i n terms of b i o a v a i l a b i l i t y and i n t e s t i n a l a b s o r p t i o n . These s t u d i e s were conducted using human volunteers and guinea p i g experimental models (]_,2_)· P r i o r to our work, absorption of v i t a m i n C from i n t e s t i n e was b e l i e v e d to be p a s s i v e , i . e . , not i n v o l v i n g a c t i v e t r a n s p o r t . Cont r a r y to t h i s b e l i e f , r e s u l t s from our i n v i v o p e r f u s i o n s t u d i e s on the s a t u r a t i o n k i n e t i c s r e l a t i n g to the i n t e s t i n a l a b s o r p t i o n of pharmacological doses of a s c o r b i c a c i d i n human volunteers and guinea pigs demonstrated t h a t i n t e s t i n a l absorption of a s c o r b i c a c i d i s accomplished by an a c t i v e t r a n s p o r t mechanism, supporting the observations made p r e v i o u s l y by Stevenson {3). The observed a c t i v e t r a n s p o r t of a s c o r b i c a c i d showed parameters c h a r a c t e r i s t i c of the phenomenon of s a t u r a b i l i t y , i . e . , as the dose of v i t a m i n C presented to the i n t e s t i n e i s i n c r e a s e d , the r e l a t i v e p r o p o r t i o n of a s c o r b i c a c i d absorbed showed a decrease. The most e f f i c i e n t a b s o r p t i o n of the v i t a m i n was observed when amounts n e a r l y i d e n t i c a l to t h a t present i n orange j u i c e were presented to the i n t e s t i n e . These observations were f u r t h e r corroborated by s t u d i e s on the a b s o r p t i o n of v i t a m i n C i n v i t r o on i s o l a t e d jejunum and ileum segments of guinea p i g w i t h i n t a c t v a s c u l a r supply using experimental guinea p i g models. These s t u d i e s , i n a d d i t i o n to establishment of the a c t i v e absorption of v i t a m i n C by i n t e s t i n e , provided c o n c l u s i v e evidence t h a t human volunteers perfused w i t h pharmacological doses of vitamin C absorbed the v i t a m i n l e s s e f f i c i e n t l y . Furthermore, i t was shown that the amount of v i t a m i n C present i n orange j u i c e i s near optimum i n terms o f i t s e f f i c i e n t absorption by i n t e s t i n e , and the pharmacol o g i c a l doses o f v i t a m i n C s u p p l i e d to human volunteers would appear to be of l i t t l e or no a d d i t i o n a l n u t r i t i o n a l value and may even be d e t r i m e n t a l . F o l i c A c i d . C i t r u s j u i c e both i n frozen or f r e s h form i s a r i c h and s t a b l e source of f o l a t e . The presence of vitamin C i n orange j u i c e p r o t e c t s i t from o x i d a t i o n and, u n l i k e other n u t r i t i o n a l sources of f o l a t e , the f o l a t e i n orange j u i c e i s not subj e c t e d to d e s t r u c t i o n caused by cooking of f o o d s t u f f . Research conducted i n our l a b o r a t o r i e s has c l e a r l y e s t a b l i s h ed t h a t , i n a d d i t i o n to being r i c h i n f o l a t e , c i t r u s j u i c e
In Citrus Nutrition and Quality; Nagy, Steven, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
2.
BAIG AND CERDA
Role of Citrus in Health and
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Disease
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contains N-5 methyl t e t r a f o l a t e as the most predominant chemical form, which i s m e t a b o l i c a l l y a c t i v e and most r e a d i l y a v a i l a b l e . I t s n a t u r a l occurrence i s unique i n c i t r u s f r u i t s (4-6). Further more, by employing t r i p l e lumen p e r f u s i o n techniques, i t was shown t h a t diphenylhydantoiη does not i n f l u e n c e the absorption of c i t r u s f o l a t e i n human v o l u n t e e r s . This may be c l i n i c a l l y s i g n i f i c a n t , s i n c e diphenylhydantoiη i n dosages s u f f i c i e n t to c o n t r o l e p i l e p t i c s e i z u r e s i n f l u e n c e s absorption o f forms of f o l a t e present i n other food sources. Vitamin B-6. Comparative s t u d i e s on the b i o a v a i l a b i l i t y of s y n t h e t i c and n a t u r a l l y o c c u r r i n g forms o f vitamin B-6 found i n orange j u i c e have demonstrated t h a t the absorption of v i t a m i n B-6 from orange j u i c e i n human volunteers i s not e f f i c i e n t when com pared w i t h the s y n t h e t i c forms of t h i s vitamin ( 7 ) . These obser v a t i o n s are s i m i l a r to the f i n d i n g s o f others ( 8 j t h a t natural n u t r i t i o n a l sources c o n t a i n the B-6 l a r g e l y i n bound form and cooking o f f o o d s t u f f enhances the b i o a v a i l a b i l i t y of t h i s v i t a m i n i n animals. N a t u r a l l y o c c u r r i n g vitamin B-6 i s g e n e r a l l y bound to p r o t e i n s (9), however c i t r u s f r u i t , which contains s u b s t a n t i a l amounts o f b i o a v a i l a b l e forms of vitamin B-6, i s low i n p r o t e i n contents. Further i n v e s t i g a t i o n s on the nature o f the chemical component bound to vitamin B-6 found i n c i t r u s f r u i t have demon s t r a t e d t h a t i n c i t r u s f r u i t v i t a m i n B-6 i s bound to a small (molecular weight:
