Recovery and Utilization of Byproducts from Citrus Processing Wastes

Chapter 29 Recovery and Utilization of Byproducts from Citrus Processing Wastes 1

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 10, 2015 | http://pubs.acs.org Publication Date: September 7, 1989 | doi: 10.1021/bk-1989-0405.ch029

L. Wicker, H. E. Hart, and M. E. Parish University of Florida, Institute of Food and Agricultural Science, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850 Growth and microbial production of by-products offers a practical alternative use of citrus processing waste. The unique physico-chemical properties of citrus peel and pulp residue provides an underutilized resource. Reports of fermentation by-products of microbial growth on dried peel or by submerged culture include c i t r i c acid, glutamic acid, riboflavin, and cobalamin. Single cell protein constitutes the bulk of research in value added processing of citrus waste. Typically, the protein content of single cell biomass can be increased five fold through fermentation processes. Hydrolytic enzymes, such as polygalacturonase, pectinesterase, cellulase, lyase, and xylanase not only represents a fermentation resource, but these enzymes are also responsible for increases in the amount of fermentable sugars. Soluble sugars can be used as substrate for other processes and can increase the yield of endogenous products not easily recovered from the cell structure. Utilization of many agroindustrial wastes to produce value added products is receiving c r i t i c a l evaluation. The high content of carbohydrate relative to content of protein presents a challenge to develop higher value products economically. Currently, i f fruit and vegetable processing waste cannot be dried or utilized fresh for cattle feed, i t must be disposed at land f i l l sites. Disposal of fruit and vegetable processing waste then has a negative impact on the economic value as well as the environment. 1

Current address: Department of Food Science and Technology, The University of Georgia, Athens, GA 30602 0097-6156/89/0405-0368$06.00/0 c 1989 American Chemical Society

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


29. WICKER ET AL.

Recovery and Utilization of Byproducts

Citrus production accounts for nearly half of the t o t a l f r u i t and vegetable production. According to a g r i c u l t u r a l s t a t i s t i c s , 13.8 and 15.2 m i l l i o n metric tons of c i t r u s and non-citrus f r u i t , respectively, were produced i n the U.S. i n 1987/88; of this amount, 9.3 m i l l i o n metric tons were processed (1). If 50% of the weight i s waste (2), then t h i s equates to about 4.9 m i l l i o n metric tons of c i t r u s waste i n 1987/88. Thus, a large concentration of f r u i t and vegetable processing waste i s l o c a l i z e d within the c i t r u s industry and provides an excellent model for production of value added products by further processing of f r u i t and vegetable wastes. Citrus processing wastes are high i n carbohydrate r e l a t i v e to the protein content. The proximate composition of dried lemon waste i s 68% carbohydrate, 18.5% f i b e r , 7% protein, 3.6% ash, 3.5% l i p i d , and 0.3% soluble reducing sugars (3). The carbohydrate composition of Pineapple orange and Marsh grapefruit i s given i n Table I. The d i s t r i b u t i o n between hemicellulose, c e l l u l o s e , pectin, and l i g n i n i s 15%, 39%, 35%, and 12%, respectively, i n Pineapple oranges. In Marsh grapefruit the d i s t r i b u t i o n i s 13%, 32%, 41%, and 14%, respectively (4). Juice v e s i c l e s and peel material not used as ingredients or processing aids i n food products (5) are usually processed into c a t t l e feed. Comminuted peel, j u i c e sacs, segments, and seeds are mixed with lime, pressed to recover the "press liquor", dried, and pelleted.

Table I.

Polysaccharide Composition i n Pineapple Orange and March Grapefruit Residue

g/100

g Fresh Component

Fiber Fraction Orange Hemicellulose Cellulose Pectin Lignin Total

a

6.6 17.6 15.5 5.2 44.9

Grapefruit 5.6 13.7 17.7 6.1 43.1

Adapted from Braddock and Graumlich (4). Values reported are t o t a l of respective f r a c t i o n i n peel, j u i c e sacs, segments and seeds.

Recent increases i n energy costs have almost made drying of c i t r u s waste cost i n e f f e c t i v e . U t i l i z a t i o n of f r u i t and vegetable processing waste material by microbial fermentation (6) for the production of other higher value products offers one solution to food and energy requirements. Fermentation by-products of microbial growth by submerged culture or s o l i d state fermentation include vitamins, amino acids, h y d r o l y t i c enzymes, and single c e l l


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protein. In addition to lowering disposal costs, enhancement of product value can be p o t e n t i a l l y r e a l i z e d . Fermentation of c i t r u s processing wastes without use of exogenous microorganisms or supplementation has been evaluated as a means to increase the n u t r i t i v e quality of c i t r u s waste for c a t t l e feed. It i s a low technology process with minimal process control. Ensilage of c i t r u s peel and pulp waste was evaluated as a means to use c i t r u s waste as ruminant feed (7). During ensilage, the authors reported a loss i n dry matter weight of 40.6%. Soluble carbohydrates and gas accounted for 7.5% and 33.1%, respectively, of the loss i n dry matter weight. In a subsequent study (8), the authors studied the loss of t o t a l sugar during ensilage and storage. The glucose content decreased from about 25.8% of the t o t a l sugar to less than 1% during ensilage. In the stored seepage, there was an i n i t i a l decline followed by an increase i n sugars to the i n i t i a l l e v e l . The authors postulated that the increase i n sugar content was due to hydrolysis of polysaccharide. Retention of the seepage within the ensilage during storage was suggested as a means to retain the n u t r i t i v e value. The major fermentation products i n ensilage of pre-dried shomouti peel were i d e n t i f i e d as ethanol (16%), l a c t i c acid (3%), and acetic acid (3%) (9). The dominant microbial populations were l a c t o b a c i l l i and yeasts. It was postulated that the yeasts produced most of the ethanol and b a c t e r i a l a c t i v i t y was i n h i b i t e d by pH values less than 3.6. Selective i n h i b i t i o n of the yeasts could conceivably prevent seepage and n u t r i t i v e losses. Microorganisms that grow on c i t r u s processing wastes and produce measurable quantities of by-products have been isolated from r o t t i n g lemons, decaying leaves, s o i l , infected vegetable tissue, orange peels, r i c e husks, p a r t i a l l y rehydrated c i t r u s p e l l e t s , or from personal l i b r a r i e s . Fermentation v i a exogenous microorganisms i s most common with submerged, aerobic fermentations, although there are reports of s o l i d state fermentations of c i t r u s waste to recover by-products. Production of Single C e l l Protein

(SCP)

Submerged Culture. The production of single c e l l protein (SCP) has received the bulk of attention for recovery of value added products. SCP production i s vastly influenced by the i n i t i a l substrate concentration and composition of soluble sugars. The e f f i c i e n c y of acid vs. enzymatic hydrolysis of Mandarin orange peel to enhance production of reducing sugars as substrate f o r SCP was evaluated and i t was observed that enzymatic hydrolysis resulted i n more e f f i c i e n t release of reducing sugars (10). Enzymatic hydrol y s i s was also determined to result i n more e f f e c t i v e release of soluble solids into the press liquor of c i t r u s waste than did conventional liming treatment (11). Moreover, the sugar content of the press liquor hydrolysates d i f f e r e d markedly. V i r t u a l l y no arabinose or xylose i s s o l u b i l i z e d by lime treatment of peel, whereas 59.7 and 9.2 mg/g dry weight press liquor, respectively, were released following treatment with commercial pectinase and c e l l u l a s e . About three times the amount of fructose and glucose were detected i n peel extracts by enzyme treatment but the



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Recovery and Utilization ofByproducts

371

difference i n galactose and galacturonic acid content were not as great as from the lime treatment (11). The u t i l i z a t i o n e f f i c i e n c y and growth y i e l d from reducing sugars was evaluated for Saccharomyces, Candida, Debaryomyces, and Rhodatorula. Of these, Rhodatorula was better for SCP production but sugar u t i l i z a t i o n e f f i c i e n c y was better i n the Debaryomyces (12). The growth parameters of Memmononella echinata and Fusarium rosuerm of l y o p h i l i z e d orange peel powder (LOPP) i n a slurry system were compared with those of other organisms grown on different substrates. Clementi et a l . (12) reported that the apparent s p e c i f i c growth rates appeared to depend on the i n i t i a l substrate concentration for LOPP. The s p e c i f i c growth rate was obtained from a plot of protein dry weight vs. time. Values of s p e c i f i c growth rate for orange peel were similar to those of other substrates evaluated such as acid and a l k a l i treated sawdust and a v i c e l . Bioreactor design f o r laboratory scale production (10L) of SCP from orange peel by Fusarium avenaceum was optimized to achieve maximum protein production i n less than eight hours (13). Enhancement of substrate u t i l i z a t i o n and SCP production may occur from concerted u t i l i z a t i o n of fermentation by-products. If Aspergillus niger were introduced 24 hours p r i o r to inoculation with Sporotrichum pulverulentum, then nearly 35% higher protein y i e l d s were obtained (3). If introduced simultaneously, the authors speculated that accumulation of glucose and cellobiose i n h i b i t e d cellulase. a c t i v i t y by j>. pulverulentum and decreased protein y i e l d s . Although the A. niger has a weak c e l l u l a s e system, i t has high pectinase a c t i v i t y with some 3-glucosidase a c t i v i t y . U t i l i z a t i o n of glucose and cellobiose by A. niger minimizes the i n h i b i t i o n of the c e l l u l a s e a c t i v i t y . Under optimized conditions and i n mixed culture, the crude protein content of the produced biomass was increased from 7% to 36%. S u f f i c i e n t nutrient supplementation and fermentation control i s also c r i t i c a l to SCP production. In submerged fermentation of Sporotrichum pulverulentum i n single culture on dried Valencia orange peel, biomass containing nearly 32% protein was produced (14). The composition of the media and c u l t i v a t i o n conditions were similar except that inorganic nitrogen as ammonium sulfate and phosphate as dibasic potassium phosphate, at 2 g/L each, were twice as high i n the fermentation i n single culture (14) than i n mixed culture 03). Whereas, the source of inorganic nitrogen did not affect large differences i n the crude protein production, pH values less than 5.0 had an adverse effect (14). Although the i n i t i a l pH of the mixed culture fermentation (3) was adjusted to pH 4.6, the pH decreased to 3.2. The combination of mixed culture to minimize i n h i b i t i o n of the S_. pulverulentum c e l l u l a s e system, control of pH near 5.0, and s u f f i c i e n t mineral supplementation could result i n higher SCP y i e l d s . However, single culture offers simpler process control and determination of the optimum stage of growth of the f i r s t culture before introduction of the second culture i s not necessary. Furthermore, S_. pulverulentum i s thermotolerant and a doubling of protein production was observed with a 10°C increase i n incubation temperature (14). Fermentation of the press j u i c e of Citrus unshuii Marcovitch by 125 strains of yeasts was conducted (15). C e l l growth was near


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QUALITY FACTORS OF FRUITS AND VEGETABLES

35 g/L and a crude protein content was near 45% at three days fermentation for two species of Candida and one of Saccharomyces. The highest y i e l d of c e l l s and crude protein content was obtained at an optimized r a t i o of: peel dry matter (50):urea (5): dibasic potassium phosphate (1). Growth of a Fusarium i s o l a t e on dried c i t r u s peel i n slurry fermentation at 50 g/L yielded 38 g/L i n 5 L fermentors (16). Further, the biomass was approximately 25 g/L protein. Characterization of the amino acid p r o f i l e indicated high quality protein with methionine as the l i m i t i n g amino acid. High biomass y i e l d s were reported when dried sweet orange residue, supplemented with NaHO^, ΙΟ^ΡΟ^, MgSO^, F e C l and (NH.^SO^, was fermented for 12 hours with Saccharomyces cerevisiae (17;. A biomass y i e l d of 31.6% and a crude protein content of 57.6% was reported.


2 >

Solid State Fermentation. Solid state fermentation of c i t r u s waste i s less common and requires aeration for p r a c t i c a l a p p l i c a t i o n . In fermentation of orange peel by Agrocybe aegerita, an increase i n t o t a l nitrogen was observed only after 84 days; i f orange peel were inoculated with A r m i l l a r i e l l a meIlea, an increase was observed after 70 days (18). A more r e a l i s t i c fermentation time of two days was reported using orange peel inoculated with Candida u t i l i s (19) and Aspergillus niger (20). Using comminuted orange peel supplemented with mineral s a l t s and a tumbling device, an increase was observed i n protein content of the dry matter from 7.3% to 18.5% (19). Stationary fermentation of orange peel i n trays to increase surface area with Aspergillus niger resulted i n a similar increase i n the protein content of dry matter (20). Solid culture of an Aspergillus niger resulted i n the production of 4.9 mg/mL of e x t r a c e l l u l a r protein on orange peel, which was about three times that grown on wheat bran (1.7 mg/mL) (21). Recovery of Organic Acids and

Vitamins

Bioconversion of high value products such as vitamins, organic, and amino acids has been most successfully exploited by the pharma c e u t i c a l industry. The use of c i t r u s wastes as a substrate for fermentation of these types of products has recently received attention. Successful a p p l i c a t i o n depends on removal of non s p e c i f i c i n h i b i t o r y agents from the peel, press residue, and d i s t i l l a t i o n residue by ion exchange or by physical separation. Organic Acids. The a b i l i t y of 33 strains of yeast to grow and produce pyruvic acid using dried c i t r u s peel as a substrate was evaluated (22). Debaryomyces coudertii IFO 1381 and Candida u t i l i s IFO 0396 produced y i e l d s of pyruvic acid near 82 mg/100 mL a f t e r 24 hours of fermentation at 30°C. Fermentation conditions were optimized with respect to nitrogen source (0.5% ammonium sulfate, dibasic phosphate concentration (0.1%), yeast extract concentration (0.01%), calcium carbonate concentration (1.0%), and magnesium sulfate concentration (0.01%). Pretreatment of c i t r u s peel powder with the sodium form of Amberlite IR-120B was observed to enhance pyruvic acid production. Under optimized conditions, a maximum of



29. WICKER ET AL.


373

970 mg pyruvic acid/100 mL could be produced with I), c o u d e r t i i i n 48 hours of fermentation (22). The use of the residue following liming and pressing of peel has also been evaluated. Citrus molasses was not a suitable substrate for c i t r i c acid production by Aspergillus niger (NRRL 599) (23). The authors speculated that excessive levels of cations such as copper and iron inhibited c i t r i c acid synthesis since ion exchange treatment improved production. A procedure was described to prepare c i t r u s molasses as a substrate for glutamic acid production by commercially used fermentation methods (24). After liming and pH adjustment to 6.0-7.0, press j u i c e was b r i e f l y heated at 90°C and the sediment removed by centrifugation. The treated press j u i c e was lower i n calcium and other i n h i b i t o r y agents and could be more easily concentrated to increase the sugar content (Table I I ) . Vitamins. Fermentation of c i t r u s molasses by Eremothecuim ashbyii (NRRL 1363) produced nearly 720 μ grams/mL r i b o f l a v i n with 7-9 days of fermentation under optimal conditions (23). Parameters c r i t i c a l to optimal r i b o f l a v i n production were i d e n t i f i e d as removal of i n h i b i t o r y agents from concentrated press liquor by f i l t r a t i o n , pH control i n a narrow range of 7-8, and adequate levels of reducing sugars. D i s t i l l a t i o n residue from recovery of orange o i l has been used as substrate for production of cobalamin (Vitamin Propionibacterium freudenreichii and Propionibacterium shermanii fermentation (25). By f i l t r a t i o n of the d i s t i l l a t i o n residue, pH adjustment to 7.0 with NaOH, and use of a two-stage, anaerobic to aerobic fermentation, nearly 6.35 mg/L of cobalamin were produced i n 192 hours of fermentation (Table I I ) . Recovery of Endogenous Products Limonene. Use of fungal cultures which produce hydrolytic enzymes were used to increase the y i e l d of endogenous products i n c i t r u s . Enzymatic digestion of plant c e l l wall structures or other sub c e l l u l a r structures enhances s o l u b i l i z a t i o n of these by-products. In an attempt to increase the y i e l d of limonene, c i t r u s peel was soaked i n fungal cultures of Neurospora crassa and Aspergillus t e r r i u s for 2.5 hours (26). The fungal culture f i l t r a t e s were p a r t i c u l a r l y r i c h i n xylanase and amylase, but also contain s i g n i f i c a n t amounts of polygalacturonase and c e l l u l a s e s . The y i e l d of essential o i l recovered by steam d i s t i l l a t i o n was increased about 54% from 1.3 to 2.0 mL/100 g of orange peel i n the fungal treated samples than i n the control. Pectin. Commercial extraction of pectin from c i t r u s involves treatment of c i t r u s waste at pH extremes with concentrated acids. In addition to the harsh extraction conditions, not a l l c i t r u s waste i s amenable to conventional pectin extraction. Mandarin orange peel becomes j e l l y - l i k e on heating and separation of pectin from the residue i s d i f f i c u l t (27). Milder extraction conditions and more e f f e c t i v e extraction has been reported i f mandarin c i t r u s peel was suspended i n water with Trichosporon pencillatum for 15 to



C

b

The quantity of product i s reported i f given by authors. data i s denoted by "+". Submerged culture fermentation. Solid substrate fermentation.

21

27

26

23

Qualitative presentation of

Soluble sugars

Dried orange

Aspergillus niger

20-25 g/kg

Trichosporon penicillatum SNO-3

Pectin

Comminuted orange peel Comminuted orange peel

700 mg/L

20 mg/kg

Riboflavin

25

6.35 mg/L

Vitamin

Limonene

residue

distillation

Filtered

Aspergillus terreus Neurospora crassa

Eremothecium ashbyii NRRL 1363

residue

distillation

Filtered

Propionibacteurium shermanii ATCC 13673

22

970 mg/100 mL

Pyruvic acid

Dried peel

Debaryomyces c o u d e r t i i

Ref.

Product

Quantity

Production of Value Added Products by Microbial Fermentation of Citrus Processing Wastes

Substrate

Microorganism

Table I I .



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20 hours at 30°C (27). Yields of 20 to 25 g pectin/kg of peel were reported and represents about 100 to 110% of the y i e l d obtained by the conventional method. The pectin extracted by t h i s method had similar chemical and physical properties as commercial pectin and pectin extracted from Mandarin orange by acid. One notable difference was the neutral sugar content of pectin extracted by fermentation was twice that extracted by acid and four times the amount detected i n commercial pectin. Although the molecular weight of the pectin extracted after fermentation was nearly the same as that determined f o r the commercial pectin, the molecular weight of acid extracted pectin from Mandarin orange was nearly half that extracted after fermentation. Soluble Solids. The hydrolysis of f r u i t and vegetable processing waste i s the result of a concerted action of multi-enzyme systems. The commercial enzymes t y p i c a l l y are not standardized with respect to secondary enzymatic a c t i v i t i e s , which may v a s t l y a f f e c t the rate and extent of hydrolysis. Since a spectrum of polysaccharide degrading enzymes i s required f o r the bioconversion of f r u i t and vegetable processing waste, single or mixed cultures of microorganisms grown on the substrate to be hydrolyzed may produce the most e f f e c t i v e primary and secondary h y d r o l y t i c enzyme system. An Aspergillus niger fungal culture was screened f o r the a b i l i t y to produce enzymes which would macerate mandarin orange peel after growth on wheat bran or mandarin orange peel i n submerged or s o l i d state culture. Although no attempt was made to recover hydrolytic enzymes, a c t i v i t y was monitored by evaluation of the maceration a c t i v i t y and the increase i n reducing sugars (21) (Table I I ) . The production of reducing sugars and t o t a l sugars i n either l i q u i d or s o l i d culture on orange peel was about h a l f that grown on wheat bran. Correspondingly, the macerating value (ratio of f i n a l mass to i n i t i a l mass) was less when Aspergillus was grown on orange peel. The macerating value of the enzymes produced on wheat bran were comparable to commercial fungal preparations. Recovery of Hydrolytic Enzymes A procedure to produce pectinases from lemon peel by s o l i d state fermentation with an Aspergillus species was described (28). Comparison f o r e f f i c i e n c y of c l a r i f i c a t i o n of the culture f i l t r a t e prepared by the authors with a commercial preparation showed that the two preparations were s i m i l a r . Optimum results f o r polygalacturonase and pectinesterase a c t i v i t y were observed when the lemon peel was pretreated by c a r e f u l drying at 100°C. Negative effects of temperature were observed when the peels were dried at a f i n a l temperature of 120°C. Washed peel had a negative impact on p e c t i n esterase a c t i v i t y but no effect on polygalacturonase a c t i v i t y . The authors speculated that washing removed some co-factor e s s e n t i a l for pectinesterase but not polygalacturonase synthesis. However, i t has been shown that removal of water soluble carbohydrates from the peel by commercial leaching also removes approximately h a l f of the endogenous pectinesterase (4). Unless s p e c i f i c steps were taken to d i s t i n g u i s h fungal or plant pectinesterase, the decrease i n pectinesterase a c t i v i t y observed by the authors could be due to



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QUALITY FACTORS OF FRUITS AND

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a leaching e f f e c t of endogenous pectinesterase. In addition, temperatures at 120°C may have p a r t i a l l y denatured some pectic enzyme a c t i v i t y (Table I I I ) . An Aspergillus species, previously isolated from wetted c i t r u s p e l l e t s , was grown on untreated Valencia f i n i s h e r pulp (29) (Table I I I ) . In inoculated pulp, protease a c t i v i t y , determined by a zone of d i f f u s i o n on casein-agarose plate, was observed after 24 hours which was sustained for 72 hours. In inoculated samples, polygalacturonase a c t i v i t y was optimal at 24 hours i f the pulp was supplemented with 1% exogenous c i t r u s pectin. In the absence of exogenous pectin, optimal polygalacturonase a c t i v i t y was observed between 72 and 96 hours. It was noted that optimal polygalacturonase a c t i v i t y preceded the onset of l i q u e f a c t i o n and syneresis by about 24 hours. The a b i l i t y of two strains of Lachnospira multiparus to grow on polygalacturonic a c i d , 36.8% e s t e r i f i e d apple pectin, or 73.4% e s t e r i f i e d c i t r u s pectin and produce pectinesterase, polygalacturonase, and pectin lyase was evaluated (30) (Table I I I ) . The author noted that whereas low methoxyl pectin and polygalacturonic acid are the preferred substrates for polygalacturonase a c t i v i t y , no polygalacturonase production was detected when _L. multiparus was grown on any of the three substrates. Pectin lyase and p e c t i n esterase a c t i v i t i e s were both detected on a l l three carbon sources, although the lyase a c t i v i t y was low on the polygalacturonic acid. Since the nature of the pectin substrate had no effect upon production of pectinesterase, S i l l e y speculated that pectinesterase i s a constitutive enzyme and that the esterase and lyase could exist as a single inducible complex. An Aspergillus niger, i d e n t i f i e d as A. niger 35-1 was selected for evaluation for production of hydrolytic enzymes with mandarin orange peel (31) (Table I I I ) . Enzyme a c t i v i t i e s for p e c t i n esterase, amylase, xylanase, and carboxymethylcellulase were low for a l l strains evaluated, whereas polygalacturonase a c t i v i t y was r e l a t i v e l y high i n several s t r a i n s , 35-1 was selected as one of the best polygalacturonase producers. The polygalacturonase was p a r t i a l l y characterized. Optimal polygalacturonase a c t i v i t y was observed at pH values between 2.5 to 4.0 and was 95% inactivated at pH 6.5. The optimal growth temperature was determined to be 55°C with an estimated 50% a c t i v i t y loss at temperatures near 70°C. Production of polygalacturonase was optimized with respect to concentration of mandarin orange peel and nitrogen source and concentration. Concentrations of peel higher than 5% were inhibitory and ammonium sulfate at 0.7% was optimum for polygalacturonase production. However, production of xylanase was optimal with sodium n i t r a t e as the nitrogen source. The reduction i n reducing and t o t a l sugars and the increase i n mycelial growth coincided with an increase i n polygalacturonase and xylanase a c t i v i t y . Interestingly, the authors noted that although the optimal concentrations of peel and ammonium sulfate coincide with an increase i n polygalacturonase a c t i v i t y , there i s not a corre-


29.

WICKER ET AI»


Table I I I .

P r o d u c t i o n o f P o l y s a c c h a r i d e D e g r a d i n g Enzymes by M i c r o b i a l of C i t r u s P r o c e s s i n g Wastes

Microorganism

Product

A s p e r g i l l u s sp.

D r i e d and ^ undried peel

PME PG

A s p e r g i l l u s sp.

Valencia ^ j u i c e sacs

Protease PG

Lachnospira D15d

HM c i t r u s pectin

PME

29

30

PME PG j PL

2.16 U/mL 0 8.58 U/mL

30

Dried Mandarin orange p e e l

PME PG CMC'ase Xylanase Amylase

0.26 2.15 0.06 0.58 0.13

31

Dried Mandarin orange p e e l

Endo-PGl Endo-PGlI Exo-PG

Valencia ^ j u i c e sacs

Recovery and Utilization of Byproducts from Citrus Processing Wastes

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