533
Ind. Eng. Chem. Prod. Res. Dev. 1982,27, 533-536
Table IV. Group Solubility Parameters
(1)Magnesia cements, primarily magnesium oxychloride, when formulated at lower viscosity can be handled more easily. parameter (2) Organosilanes, organosilanols, and organosilanol salts have been found to be effective viscosity reducers. organosilicon compound 6, structural formulaa (~ a l / c m ~ ) " ~ (3) The selection of operable organosilicon compounds is dependent upon solubility characteristics of groups Viscosity Reducers bonded directly to silicon. 6.41 H,N( CH,),Si( Me),( OMe) H,N(CH,),SiMe( OEt), 6.74 (CH,CH,CHOHCH,),N( CH,),Si( OEt), 6.95 Acknowledgment H,N(CH,),Si(OEt), 7.19 CH,CH,CHOHCH,NH( CH,),Si(OEt), 7.21 The authors wish to thank PPG and the Director of CH,CH,CHOHCH,S( CH,),Si( OEt), 1.24 Coatings and Resins Research for supporting this work. CH,=C( CH,)COO(CH:,),Si(OMe), 7.33 H,N(CH,),NH(CH,),Si(OMe), 7.36 Literature Cited CH,CH,CHOHCH,NHCONH( CH,),Si( OEt), 1.43 [( EtO),Si(CH,),NHCH,CHOHCH,OCH~CH,], 7.52 Boberski, W. 0.;Chang, W.-H.; Seiner, J. A.; Petracca, V. G. U . S . Patents group soh bility
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 9, 2015 | http://pubs.acs.org Publication Date: December 1, 1982 | doi: 10.1021/i300008a004
"\
CH,--CH,CH,O( CH,),Si(OMe), Ineffective as Viscosity Reducers CH,Si(OMe), H,NCONH( CH,),Si( OEt), a Et = CH,CH,; Me = CH,.
I . 83
5.33 8.61
the conclusion that when this group has a working parameter of solubility between about 6.2 and 8.0 (cal/ cm3)lI2,the additive is an effective viscosity reducing agent. Conclusions The results of this paper summarize rather easily.
11.
4 174 228 and 4 174 229, 1979. Bunn, C. W. J. Polym. Sci. 1955, 16, 323. Hoy, K. L. J. Paint Techno/. 1970, 42, 78. Lloyd, W. G.; Durocher, T. E. U.S.Patent 3 130 174, 1984. Prior, W. L. U.S. Patent 3320077, 1967. Small, P. A. J. Appl. Chem. 1853, 3 , 71. Sorei, M. C. R . Hebd. Seances Acad. Sci. 1887, 65, 102. Van Krevelen, D. W. "Propertles of Polymers"; Elsevier Publishing Co.: New York, 1972; Appendix I .
Receiued f o r reuiew April 16, 1982 Accepted June 1, 1982 This paper was presented at the 183rd National Meeting of the American Chemical Society, Las Vegas, NV, Mar 28-Apr 2,1982.
Symposium on Flavor Chemistry of Fermented Foods and Feed Products E. Seitz, Chairman 182nd National Meeting of the American Chemical Society New York, New York, August 1981
Flavor Chemistry of Fermented Peanuts Larry R. Beuchat Department of Food Science, University of Georgia, Agricultural Experiment Station, Experiment, Georgia 302 72
Fungal fermentation of peanut press cake to produce oncom in Indonesia has been carried out on a wide scale for centuries. Two molds, Neurospora sitophila and Rhizopus oligosporus , are most commonly used to prepare a semisolid product having a fruity, alcoholic flavor when fresh, but described as taking on a mincemeat or almond flavor when fried in oil. Depending upon the conditions of fermentation and the mold employed, peanut constituents may be broken down and utllized to various degrees. Molds used in traditional peanut fermentation schemes are active lipase and carbohydrase producers. Simple sugars may be completely utilized. All of the metabolic activities contribute to changes in the flavor profile of peanuts. Recent investigations have focused on the sensory qualities of peanut miso and fermented peanut milk. While flavor characteristics of these products differ somewhat from those of soybean miso and fermented dairy products, respectively, potential exists for the development of new, highly acceptable fermented peanut products.
Introduction Fermented foods and beverages contribute significantly to the diets of many people throughout the world. Oilseed and cereal cake fermentation products, sometimes called
vegetable cheeses, are especially prevalent in Southeast Asia and parts of Africa. Oncom (ontjom, lontjom) is a fermented peanut press cake product very popular in Indonesia (Beuchat, 1976,1978). Two different fungi may
0196-4321/82/1221-0533$01.25/00 1982 American Chemical Society
534
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 4, 1982
Extract oil from peanuts Soak in wate; about I day Remove excess oil, steam p r e s s cake
I
P r e s s into bamboo frame
Inoculate w i t h Neurospora sitophih Ferment ( i to 2 days 1 I
t
ON C O M Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 9, 2015 | http://pubs.acs.org Publication Date: December 1, 1982 | doi: 10.1021/i300008a004
Figure 1. Flow sheet for the production of oncom.
be used to produce oncom. Neurospora sitophila is most often used and results in an orange or pink product while Rhizopus oligosporus, also used to ferment soybeans in the preparation of tempeh, produces a white oncom (Hesseltine, 1965). Although oncom has been prepared and consumed in Indonesia for centuries, the biomodifications occurring during its fermentation which contribute to flavor development are far from being understood. Aside from interested groups at the U.S. Department of Agriculture, Northern Regional Research Laboratory in Peoria, IL, the New York State Agricultural Experiment Station, Cornel1 University, Geneva, NY, and the Tropical Products Institute in England, research efforts directed toward characterizing chemical, organoleptic, and nutritional properties of fermented peanut press cake have been meager. In recent years our laboratory has explored some of the complex changes occurring in peanuts during fungal and bacterial fermentation. This paper presents a summary of our findings; contrasts and comparisons are made with data reported by others on peanut fermentation. These studies are easily divided into two groups, one dealing with fungal fermentation of peanuts in a solid state and the other with bacterial fermentation of liquid substrates, and the text is organized in that order. Solid State Fermentation Figure 1 shows a flow sheet for the production of oncom. After oil has been extracted from peanuts, the press cake is broken up and soaked in water for about a day. Technical press cake is low in residual oil content while village products contain considerable amounts. In either case, oil which rises to the water surface during soaking is removed. The press cake is then steamed and pressed into molds about 3 X 10 X 20 cm in size. The molds are then placed in a bamboo frame, covered with banana leaves, and inculated with either N . sitophila or R. oligosporus. Both fungi are readily available, usually from previous batches of fermented product. Neurospora is a common fungus in woody material under tropical rain forest conditions. After one or two days of standing in a shady location, the fungus has invaded the peanut mass and the oncom is ready for consumption. Constant aeration is important in the production of oncom, as are temperature, moisture content, and degree of press cake granulation. Added carbohydrate such as cassava, potato, or potato peels appears to be beneficial in the fermentation process. The finished product averages 70% moisture, 3 to 9% oil, 20 to 30% crude protein, about 4 % carbohydrate, 1% ash, and 2 % fiber.
The flavor of fermented peanut press cake has been described as fruity and somewhat alcoholic; however, the fried material takes on a mince-meat or almond flavor (Hesseltine, 1965). Oncom may also be roasted, covered with boiling water, and seasoned with salt or sugar before eating. In another fashion it is roasted, cut into pieces, and covered with a ginger sauce. While specific components which may contribute to flavor development have not been fully determined, findings from investigations of the metabolic activities of N. sitophila and R . oligosporus during fermentation do give us some basis for postulating the responsible breakdown products. A review of the proteolytic, lipolytic, and saccharolytic activities of these fungi will follow in an attempt to begin to characterize the flavor chemistry of fermented peanuts. Proteolytic Activity. The bulk of research data relating changes in protein after fermentation of peanut press cake (and oilseeds in general) with N. sitophila and R. oligosporus indicates that protein content is little altered but solubility is greatly increased. An apparent increase in percentage of crude protein has been demonstrated in peanuts fermented with the oncom fungi, in addition to Mucor hiemalis and Actinomucor elegans, both traditionally used to ferment soybeans in the preparation of a Chinese cheese called sufu, and Aspergillus oryzae, the koji mold used to produce soy sauce and miso (Quinn et al., 1975). However, there may not be an actual increase in protein weight as a result of fermentation but rather a loss of nonprotein volatiles during the fermentation process, thus accounting for proportionate increases in unaltered peanut press cake constituents. Fungal proteinase and peptidase production and activity in peanut substrates are greatly affected by pH, temperature, moisture, and ionizable salts (Wang, 1967; Wang et al., 1974). The extent to which proteins are solubilized varies; however, most reports indicate that no significant changes occur in the amino acid profiles of peanuts after fermentation. Prolonged fermentation may result in decreased lysine and methionine levels. Free amino acid contents of fermented peanuts are greatly increased over raw products. For example, the percentages of total amino acids as free in peanuts fermented for 98 h at 28 "C are about 9% and 3% for N . sitophila and R. oligosporus, respectively (Beuchat et al., 1975). One mold, Actinomucor elegans, hydrolyzed peanut protein to yield 13% free amino acids in a 4-day fermentation period. The accumulation of free amino acids and peptides in fermented peanuts results in the meaty flavor characteristic of several other fermented oilseed products. Lipase Activity. The lipolytic activity of fungi used to prepare oncom should be considered in a discussion of flavor chemistry. Both N. sitophila and R . oligosporus are active lipase producers, hydrolyzing triglycerides to yield free fatty acids which accumulate to various levels, depending on fermentation conditions. We have studied changes in total lipids, total fatty acids, and free fatty acids in full-fat peanuts fermented with N. sitophila and R. oligosporus, as well as A. oryzae, Aspergillus niger, and Rhizopus delemar, for incubation times ranging to 116 h (Beuchat and Worthington, 1974). Lipolytic activity as monitored by alkali titration of ferment extracts was essentially linear for the Rhizopus spp. throughout fermentation, while an initial lag of about 40 h was required before increases in free fatty acids were noted in ferments inoculated with N. sitophila. The distribution of fatty acids in fermented peanuts has also been studied (Table I). With the exception of slightly
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 4, 1982
535
Table I. Lipid and Fatty Acid Composition of Control and Fermented Peanuts fungus control control control N. sitophila N. sitophila A. oryzae A. niger R. oligospor 'us R. delemar
temp,
time,
"C
h
28 21 28 21 28 28 28 28
0 99 116 99 116 90 90 90 74
lipid,
fatty acid, %
%a
16:O
18:O
18:l
18:2
20:O
20:l
22:O
24:O
50.8 50.5 50.5 52.1 51.6 53.3 52.5 48.3 51.4
10.6 10.6 10.7 10.3 10.5 10.3 10.1 9.4 9.8
2.7 2.8 2.8 2.7 2.7 2.3 2.7 2.5 2.4
51.2 50.9 51.1 50.3 50.7 50.9 50.7 51.6 52.1
28.3 28.5 28.2 28.3 28.2 28.4 28.4 28.7 29.1
1.4 1.4 1.4 1.4 1.3 1.4 1.4 1.4 1.2
1.3 1.4 1.3 1.4 1.3 1.3 1.4 1.3 1.2
2.8 2.8 2.9 3.0 2.7 2.8 2.8 2.8 2.4
1.6 1.6 1.4 1.6 1.6 1.6 1.7 1.7 1.4
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 9, 2015 | http://pubs.acs.org Publication Date: December 1, 1982 | doi: 10.1021/i300008a004
a Percentage of peanut, dry weight basis; average of two determinations. average of four determinations. From Beuchat and Worthington (1974).
lower percentages of palmitic (16:O) and slightly higher percentages of oleic (181)and linoleic (18:2) acids calculated for R. oligosporus and R. delemar ferments, the remaining major fatty acids [stearic (18:0), eicosanoic ( 2 0 0 ) , eicosenoic (20:1), docosanoic (22:0), and tetracosanoic (24:0)] in lipid of peanuts fermented with N . sitophila, A. oryzae, A . niger, R. oligosporus, and R. delemar were essentially unchanged from the controls. On the other hand, the free fatty acid fractions of full fat peanut ferments contained significantly higher levels of saturated fatty acids, particularly palmitic and stearic acids, and lower levels of linoleic acid than did the total lipid extracts. These differences in free fatty acid distribution can be attributed to the action of 1,3-lipases,since saturated acids are located primarily in the 1,3 positions and linoleic acid is in the 2 position of peanut triglycerides. Oleic acid is approximately equally distributed among the three positions. To the author's knowledge, data have not been published correlating the presence or type of particular fatty acids or their reaction products to flavor and aroma development in oncom. It is well known, however, that flavor development in cocoa and dairy products is highly dependent on lipase activities of a large number of microorganisms. For example, a commercially available lipase from R. delemar, a fungus showing strong lipolytic activity in peanuts, is said to enhance flavors of dairy products. Fatty acids freed by A . elegans during fermentation of soybean curd in the preparation of sufu and by A. oryzae in miso fermentation are reported to react chemically or enzymatically with ethanol to form esters, thus providing pleasant odors to the products. An interesting study would involve the effects of changes in lipid quantity and quality on organoleptic characteristics of fermented peanuts. Carbohydrase Activity. The carbohydrate content of full-fat peanut kernels is low (12 to 18%) compared to lipid and protein contents. Removal of lipid by solvent extraction or expulsion processes results in an approximate twofold increase in remaining constituents, including carbohydrates. This carbohydrate fraction of peanut press cake is comprised largely of cellulose and simple oligosaccharides. Reducing substances generally decrease as a result of fungal utilization of low molecular weight reducing sugars as sources of energy. Organic acids which may result during breakdown of simple sugars are reported to contribute to darkening of product color and to the development of disagreeable flavors. Although the raffinose and stachyose content of peanuts is considerably lower than that of beans, often present in only trace quantities, hydrolysis of these and other oligosaccharides during oncom fermentation undoubtedly contributes to increased digestibility and decreased sweetness. We have observed that the sucrose, raffinose, and stachyose content of peanuts is essentially reduced to
Percentage of total fatty acid in peanut lipid; S o a k peanuts in NaHC030vernighi
I
Discard liquid -Drain
I
Wash peanuts, grind
I
Steep in t a p woter 4 - 5 hours Discard solids -Filter
I I min a t 121'C,
Heat I O c o o l quickly, odd 2 % lactose (wt/vol)
I
I n o c u l a t e with l a c t i c a c i d bacteria
I 4
Incubate 2-3 days a t 37' C FERMENTED
PEANUT M I L K P R O D U C T
Figure 2. Flow sheet for the production of fermented peanut milk products.
zero after 21 h of fermentation with N . sitophila (Table 11) (Worthington and Beuchat, 1974). R. oligosporus may utilize small amounts of stachyose, but only after 68 h of fermentation, and it does not utilize raffinose and sucrose. To summarize the flavor chemistry of peanuts fermented in a traditional manner to produce oncom, one can state that free amino acids and salts produced from them as well as peptides are probably significant contributing factors. Organic acids, aliphatic esters, alcohols and possibly phenols and mercaptals also are likely to be responsible for desirable flavor characteristics of oncom. Recent investigations (Shieh et al., 1982; Shieh and Beuchat, 1982) indicate that acceptable miso-like products can be prepared by replacing soybeans with peanuts. Additional studies will be necessary to characterize the flavor profiles of these products.
Liquid Fermentation Several reports exist in the literature describing procedures for preparing fermented soybean milk. Work in our laboratory (Beuchat and Nail, 1978) and in that of Dr. R. H. Schmidt at the University of Florida (Schmidt and Bates, 1976) has shown that highly acceptable fermented products can also be prepared from aqueous extracts of peanuts. The first step in preparing fermented peanut milk involves reducing undesirable beany, green, or painty offflavors characteristic of the raw kernel. These off-flavors can be reduced in peanut extracts if the whole raw peanuts are soaked in a 1% sodium bicarbonate solution for a 16-18-h period at room temperature before they are subjected to a heat treatment, ground, and filtered (Figure 2). The resulting liquid (peanut milk) may then be pasteurized
538
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 4, 1982
Table 11. Sucrose, Raffinose, and Stachyose Content of Control and Fermented Peanuts
___.-.
fungus control
fermentation time, h U
b i:
A. niger
A.oryzae
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 9, 2015 | http://pubs.acs.org Publication Date: December 1, 1982 | doi: 10.1021/i300008a004
N . sitophila
R. delemar
21 44 68 98 21 44 68 98 21 44 68 98 21 44
R . arrhizus
R . oligosporus
M. purpureus
M. hie mal is
A.elegans
68 98 21 44 68 98 21
44 68 98 21 44 68 98 21 44 68 98 21 44 68 98
g/lOO g of sample sucrose
raffinose
stachyose
6.9 5.3 5.2 0.29 0.01 0.08 0.08 0.07 0.04 T 0.05 0.03 0.02 T 0.06 0.02 0.51 0.15 0.06 5.9 6.6 7.7 9.3 5.8 6.8 6.7 6.5 5.4 5.7 7.8 9.1 0.53 0.22 0.34 0.20 5.6 5.9 6.7 6.7
0.15 0.10 0.10 0.04 0.0% ND ND 0.01 T ND ND ND ND ND T 0.04 ND ND ND 0.11 0.18 0.30 0.61 0.08 0.12 0.17 0.27 0.08 0.16 0.20 0.06 0.13 0.09 0.13 0.24 0.10 0.10 0.13 0.28
0.6 5 0.60 0.47 0.30 Te T ND 0.24 T ND ND 0.03 T
T 0.02 0.35
T ND ND 0.4 I 0.41 0.32 0.19 0.45 0.53 0.62 0.39 0.4 8 0.37 0.09 T 0.51 0.58 0.60 0.61 0.40 0.44 0.39 0.34
Unfermented samde. autoclaved. freeze-dried * Unfermented sample. not autoclaved. freeze-dried without incubation. without incubation. Unfermented sample, autoclaved, incubated 98 h a t 28 “C before freeze-drying. Not’detected. e Trace, less than 0.01 g/100 g of sample. From Worthington and Beuchat (1974).
and supplemented with lactose or other sugars before inoculating with one or more lactic acid bacteria commonly used to ferment various animal milks. After a period of incubation, the peanut milk takes on desirable organoleptic properties not unlike those associated with dairy cheese, yogurt, buttermilk, sow cream, and so on, depending upon the bacteria originally selected for inoculation. Organic acids, diacetyl, aldehydes, ketones, alcohols, and sulfurcontaining byproducts undoubtedly accumulate during the course of fermentation, although, to the author’s knowledge, positive identification of these compounds in fermented peanut milk has not been made. Sensory panel evaluations of blended, fermented peanut milks containing added sucrose and fruit flavorings have shown that these products are highly acceptable and compete favorably with flavored buttermilk (Beuchat and Nail, 1978). Fermented peanut milk substituted for buttermilk in a corn muffin recipe resulted in products with organoleptic characteristics not significantly different from those of the control. Not much definitive information on the subject of peanut fermentation has been presented here, mainly because there is not much available to present. This is a wide open field for those interested in food fermentations
and it is hoped that more researchers become actively involved.
Literature Cited Beuchat, L. R. Econ. Bot. 1978, 30, 227. Beuchat, L. R. I n “Food and Beverage Mycology”, Beuchat, L. R., Ed. A V I Publ. Co.: Westport, CT, 1978; p 224. Beuchat, L. R.; Nail, B. J. J . Food Sci. 1978, 4 3 , 1109. Beuchat, L. R.; Worthington, R. E. J. Agric. Food Chem. 1974, 22, 509. Beuchat, L. R.; Young, C. T.; Cherry, J. P. Can. I n s t . Food Sci. Techno/. J . 1975, 8 , 40. Hesseltine, C . W. Myco/og/a 1965, 57, 149. Quinn, M. R.; Beuchat, L. R.: Miller, J.; Young, C. T.; Worthington. R. E. J. Food SCi. 1975, 4 0 , 470. Schmidt, R. H.; Bates, R. P. R o c . Fk,. State Hortic. SOC. 1978, 89, 217. Shleh, Y.-Y. C.; Beuchat, L. R. J. FoodSci. 1982, 47, 518. Shleh, Y.-Y. C.; Beuchat, L. R.; Worthington, R. E.; Phillips. R. D. J. Food Sci. 1982, 47, 523. Wang, H. L. J. Bacterial. 1987, 93, 1794. Wang, H. L.; Vespa, J. 8.; Hesseltine, C. W. Appl. Microbioi. 1974, 27,906. Worthington. R. E.: Beuchat, L. R. J. Agric. Food Chem. 1974, 22, 1063.
Received for review October 15, 1981 Revised manuscript received February 19, 1982 Accepted August 13, 1982
Paper presented at the 182nd National Meeting of the American Chemical Society, New York, NY Aug 23-28, 1981; AGFD No. 48.
