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Stabilization of black truffle of Perigord (Tuber melanosporum) by high pressure treatment.
R. Hayashi and C. Balny (Editors), High Pressure Bioscience and Biotechnology 9 1996 Elsevier Science B.V. All rights reserved.
401
Stabilization of black truffle of Perigord (Tuber melanosporum) by high pressure treatment. A. E1 Moueffak a, C. Cruz a, M. Montury a, A. Deschamps b, A. Largeteau c and G. Demazeau c. aEURIA, Universit6 de Bordeaux I, 39 rue Paul Mazy, 24019 P6rigueux, France bI.S.T.A.B ,cI.H.P. Universit6 de Bordeaux I, Domaine Universitaire, 33405 Talence Cedex, France Abstract The effects of combined high pressure (550 MPa for 30 min) and low t e m p e r a t u r e (40~ 60~ and 80~ treatments on the microbial contamination and organoleptic qualities (aroma, taste and exudation) of black truffle samples were compared with those of classical thermal sterilization (100~ for 3 hours). All the high pressure t r e a t m e n t s at 40~ 60~ and 80~ caused a fungi flora inactivation and drastic reductions of the total mesophilic contamination which turns from 107 to 102 or to less than 10 CFU/g. The exudat ratio, as well as aroma, seems to p r e s e n t no significant change b e t w e e n p r e s s u r i z e d samples and sterilized ones. Described pressure t r e a t m e n t s at low t e m p e r a t u r e followed by storage at 4~ afford a method for microbial stabilization of black truffles. 1. I N T R O D U C T I O N Fresh black truffles have well recognized organoleptic qualities and can be processed through two ways : fresh (kept only few days) or sterilized (kept at room temperature). Truffles are highly fragile and t h e r m a l processing leads to a certain exudation d e t r i m e n t a l to the yield and to the organoleptic properties. Therefore, the thermal t r e a t m e n t should be limited to the minimal required for preservation. The high hydrostatic pressure preservation treatments (100 - 700 MPa) have been suggested as a soft processing technique, allowing the reduction of the t r e a t m e n t t e m p e r a t u r e s or d u r a t i o n , and also for s t a b i l i z a t i o n at low t e m p e r a t u r e [1-3]. High pressure processed foods are already commercialized in J a p a n , mainly fruit juices and m a r m e l a d e s [4]. Extension is now being u n d e r t a k e n to meat products [5], seafoods, and even "Foie Gras" [6].
402 Varied contaminations (Pseudomonas, Bacillus, fungi flora, sporas...) are present on black fresh truffles. The main objective of this preliminary study is to demonstrate the feasibility of combined high pressure/reduced temperature treatment, for the stabilization of vacuum packed, black truffle, in order to diversify its distribution and preserve its organoleptic properties. 2. MATERIALS AND METHODS Raw materials: The black fresh truffles were harvested in Dordogne (France). As usually, before t r adi t i onal t r e a t m e n t , whole samples were washed, brushed, vacuum packaged (PE/PA/PE) or tin conditionned and refrigerated at 4~ until further experiments. Experimental design: temperatures of 40~ 60~ or 80~ were used during high pressure t r e a t m e n t s , at 550 MPa for 30 min. Three batches were performed using samples kept 2 days, 8 days and 22 days at 4~ after treatment. Samples obtained from high pressure t r e a t m e n t s were compared with samples t r a d i t i o n a l l y processed by t herm al sterilization and with untreated samples. T r ad itio n al t h e r m a l treatments" ten control samples were processed by traditional thermal treatment, similar to industrial or craft ones" introduced in tins with 2 mL water, truffles were sterilized in water at 100~ for 3 hours, then cooled and stored until +4~ High pressure treatment: High pressure treatments were performed at the Interface Hautes Pressions (E.N.S.C.P.B. - L.C.S. - C.N.R.S. Bordeaux France. For each temperature (40~ 60~ and 80~ three samples were pressurized at 550 MPa for 30 min, then cooled immediatly and stored at 4~ Microbiological analysis" The microbial analysis were performed in duplicate at the same dates" 2 days, 8 days and 22 days after t r e a t m e n t s in two laboratories (EURIA and ISTAB) using the same methodology. Counting of total mesophilic aerobic flora at 30~ fungi flora at room temperature, sulfito-reductive anareobic flora, aerobic and anaerobic spore forming bacteria inlg, were performed. Aroma analysis" The analysis were carried out on unt reat ed and treated truffles and on juice of exudation. 0,2g of truffle flesh or 2mL of exudation juice were analysed by a gas chromatographic device TEKMAR (Headspace desorption- concentration - GC introduction). After separation in a Varian gas chromatograph, aromatic compounds were detected and identified in a FININGAN ITS 40, Ion trap, mass spectrometer. Some fresh, t he r m a l sterilized and pressurised samples were equally provided to truffle professionals for sensory analysis at 20 and 120 days after treatment and storage at 4~ Exudation measure" On package opening, the exudation juice was collected and weighted. Exudation was expressed as the weight ratio of exudation juice and fresh whole truffle (w/w).
403 3. RESULTS AND DISCUSSION 3.1. M i c r o b i a l effect o f t r e a t m e n t s
Results concerning the effects of high pressure and thermal treatments on microbiological contamination are given in Table 1. Sulfito-reductive anaerobic flora, anaerobic sporulated and aerobic sporulated floras don't appear in this table, for their initial population was not significative. Table 1 Effect of high pressure t r e a t m e n t on the microbiological contamination of truffles samples (CFU/g) Treatments TMAF (CFU/g) Fungi Flora (CFU/g) Storage days at 4~ Untreated Heat sterilized(100~ 550 MPa/30min. 40~ 60~ 80~
h.)
2 107 <10
8
22
8
22
<10
2 103 <10
<10
<10
<10
102 102 <10
102 102 <10
<10 <10 <10
<10 <10 <10
<10 <10 <10
<10 <10 <10
Table 1 shows that the fungi flora was totaly inactivated whatever the treatment applied even at low temperature (40~ It is well known that the fungi flora seems to be highly sensitive to high pressure [2]. Total mesophilic aerobic flora was reduced by high pressure treatment at 40~ and 60~ from 107 to 102 CFU/g. The high pressure treatment at the strongest temperature (80~ allowed a reduction of contamination similar to those obtained through traditional t h e r m a l sterilization (100~ hours) and provided a good stabilization of the product. We observed after pressurization and storage at 4~ under vacuum for 8 and 22 days, a total absence of growth for the residual contamination. 3.2. Effects o f t r e a t m e n t s o n e x u d a t i o n
Our results about exudation after 22 days expressed as percentages of fresh truffle weights are similar (between 15% to 20%) whatever the conditions used but less than the released amount of juice (25%) reported by Talou et al. [7] after thermal processing. Considering the juice aspect, we observed that the thermal processing led to a darker exudation juice than the high pressure processing, indicating a higher thermal damage of juice components. 3.3. Effects o f t r e a t m e n t s o n a r o m a a n d taste
Aromatic composition of fresh truffle seems not to be modified by high pressure treatments. High pressure t r e a t m e n t preserved in truffle some aromatic volatile components which were extracted in exudation liquid by heat sterilized treatment, as reported by Talou et al. [7]. After 21 days of storage at 4~ the olfactory and taste qualities of high pressurized seemed to be similar to those of heat sterilized ones, but an attractive characteristic was also found by professionnals for pressurized samples, according to the temperature used during high pressure processing.
404 Indeed, the best olfactive as well as taste evaluation was presented by samples pressurized at 40~ After the same delay in the same conditions, an attractive aroma close to that of a sterilized truffles was characterised for two pressurized samples one of which had been opened 21 days after processing. 4. CONCLUSION Results show that truffle bacteriological contamination could be reduced by high pressure processing at lower temperature than traditional sterilization. High pressure treatment (550 MPa, 30 min) could afford two types of new products according to the choosen temperature: on one hand at 40~ tasty truffles with organoleptic properties close to those of fresh truffles storable few weeks and on the other hand, at 80~ stabilized truffles closed to sterilized products but with less modified organoleptic properties. But, further investigations may be made to reduce the exudation by optimization of processing parameters (temperature, high pressure intensity, duration). It is also necessary to investigate more about high pressure effects on aromatic compounds and sensory aspect. 5. ACKNOWI~DGEMENTS Authors would like to thank the F6d6ration D6partementale des Trufficulteurs for supporting this work. 6. REFERENCES 1 2 3 4 5
6 7
R. Hayashi, R. Spiess and H. Schubert (eds.), Engineering and food, London :Applied Science, 2 (1989) 815. J.C. Cheftel, I.A.A., 108 (1991) 141. J.C. Cheftel, in C. Balny, R. Hayashi, K. Heremans and P. Masson (eds.), High Pressure and Biotechnology. J. Libbey/Eurotext, INSERM, LondonMontrouge, 224 (1992) 195. H. Kinugasa, T. Takeo, K. Fukumoto, T. Shinno and M. Ishihara, (eds.), High Pressure Bioscience and Food Science. Kyoto : Ei Pub. Co. (1993) 237. A. Suzuki, K. Kim, N. Homma,Y. Ikeuchi and M. Saito, in C. Balny, R. Hayashi, K. Heremans and P. Masson (eds.), High Pressure and Biotechnology, J. Libbey/Eurotex, INSERM, London-Montrouge, 224 (1992) 219. A. E1 Moueffak, C. Cruz, M. Antoine, M. Montury, G. Demazeau, A. Largeteau and F. Zuber, Int. J. Food Sci. Tech., 30 (1995) 391. T. Talou, M. Delmas and A. Gaset, Vitt. Flavor Fragr. J., 4 (1989) 109.
401
Stabilization of black truffle of Perigord (Tuber melanosporum) by high pressure treatment. A. E1 Moueffak a, C. Cruz a, M. Montury a, A. Deschamps b, A. Largeteau c and G. Demazeau c. aEURIA, Universit6 de Bordeaux I, 39 rue Paul Mazy, 24019 P6rigueux, France bI.S.T.A.B ,cI.H.P. Universit6 de Bordeaux I, Domaine Universitaire, 33405 Talence Cedex, France Abstract The effects of combined high pressure (550 MPa for 30 min) and low t e m p e r a t u r e (40~ 60~ and 80~ treatments on the microbial contamination and organoleptic qualities (aroma, taste and exudation) of black truffle samples were compared with those of classical thermal sterilization (100~ for 3 hours). All the high pressure t r e a t m e n t s at 40~ 60~ and 80~ caused a fungi flora inactivation and drastic reductions of the total mesophilic contamination which turns from 107 to 102 or to less than 10 CFU/g. The exudat ratio, as well as aroma, seems to p r e s e n t no significant change b e t w e e n p r e s s u r i z e d samples and sterilized ones. Described pressure t r e a t m e n t s at low t e m p e r a t u r e followed by storage at 4~ afford a method for microbial stabilization of black truffles. 1. I N T R O D U C T I O N Fresh black truffles have well recognized organoleptic qualities and can be processed through two ways : fresh (kept only few days) or sterilized (kept at room temperature). Truffles are highly fragile and t h e r m a l processing leads to a certain exudation d e t r i m e n t a l to the yield and to the organoleptic properties. Therefore, the thermal t r e a t m e n t should be limited to the minimal required for preservation. The high hydrostatic pressure preservation treatments (100 - 700 MPa) have been suggested as a soft processing technique, allowing the reduction of the t r e a t m e n t t e m p e r a t u r e s or d u r a t i o n , and also for s t a b i l i z a t i o n at low t e m p e r a t u r e [1-3]. High pressure processed foods are already commercialized in J a p a n , mainly fruit juices and m a r m e l a d e s [4]. Extension is now being u n d e r t a k e n to meat products [5], seafoods, and even "Foie Gras" [6].
402 Varied contaminations (Pseudomonas, Bacillus, fungi flora, sporas...) are present on black fresh truffles. The main objective of this preliminary study is to demonstrate the feasibility of combined high pressure/reduced temperature treatment, for the stabilization of vacuum packed, black truffle, in order to diversify its distribution and preserve its organoleptic properties. 2. MATERIALS AND METHODS Raw materials: The black fresh truffles were harvested in Dordogne (France). As usually, before t r adi t i onal t r e a t m e n t , whole samples were washed, brushed, vacuum packaged (PE/PA/PE) or tin conditionned and refrigerated at 4~ until further experiments. Experimental design: temperatures of 40~ 60~ or 80~ were used during high pressure t r e a t m e n t s , at 550 MPa for 30 min. Three batches were performed using samples kept 2 days, 8 days and 22 days at 4~ after treatment. Samples obtained from high pressure t r e a t m e n t s were compared with samples t r a d i t i o n a l l y processed by t herm al sterilization and with untreated samples. T r ad itio n al t h e r m a l treatments" ten control samples were processed by traditional thermal treatment, similar to industrial or craft ones" introduced in tins with 2 mL water, truffles were sterilized in water at 100~ for 3 hours, then cooled and stored until +4~ High pressure treatment: High pressure treatments were performed at the Interface Hautes Pressions (E.N.S.C.P.B. - L.C.S. - C.N.R.S. Bordeaux France. For each temperature (40~ 60~ and 80~ three samples were pressurized at 550 MPa for 30 min, then cooled immediatly and stored at 4~ Microbiological analysis" The microbial analysis were performed in duplicate at the same dates" 2 days, 8 days and 22 days after t r e a t m e n t s in two laboratories (EURIA and ISTAB) using the same methodology. Counting of total mesophilic aerobic flora at 30~ fungi flora at room temperature, sulfito-reductive anareobic flora, aerobic and anaerobic spore forming bacteria inlg, were performed. Aroma analysis" The analysis were carried out on unt reat ed and treated truffles and on juice of exudation. 0,2g of truffle flesh or 2mL of exudation juice were analysed by a gas chromatographic device TEKMAR (Headspace desorption- concentration - GC introduction). After separation in a Varian gas chromatograph, aromatic compounds were detected and identified in a FININGAN ITS 40, Ion trap, mass spectrometer. Some fresh, t he r m a l sterilized and pressurised samples were equally provided to truffle professionals for sensory analysis at 20 and 120 days after treatment and storage at 4~ Exudation measure" On package opening, the exudation juice was collected and weighted. Exudation was expressed as the weight ratio of exudation juice and fresh whole truffle (w/w).
403 3. RESULTS AND DISCUSSION 3.1. M i c r o b i a l effect o f t r e a t m e n t s
Results concerning the effects of high pressure and thermal treatments on microbiological contamination are given in Table 1. Sulfito-reductive anaerobic flora, anaerobic sporulated and aerobic sporulated floras don't appear in this table, for their initial population was not significative. Table 1 Effect of high pressure t r e a t m e n t on the microbiological contamination of truffles samples (CFU/g) Treatments TMAF (CFU/g) Fungi Flora (CFU/g) Storage days at 4~ Untreated Heat sterilized(100~ 550 MPa/30min. 40~ 60~ 80~
h.)
2 107 <10
8
22
8
22
<10
2 103 <10
<10
<10
<10
102 102 <10
102 102 <10
<10 <10 <10
<10 <10 <10
<10 <10 <10
<10 <10 <10
Table 1 shows that the fungi flora was totaly inactivated whatever the treatment applied even at low temperature (40~ It is well known that the fungi flora seems to be highly sensitive to high pressure [2]. Total mesophilic aerobic flora was reduced by high pressure treatment at 40~ and 60~ from 107 to 102 CFU/g. The high pressure treatment at the strongest temperature (80~ allowed a reduction of contamination similar to those obtained through traditional t h e r m a l sterilization (100~ hours) and provided a good stabilization of the product. We observed after pressurization and storage at 4~ under vacuum for 8 and 22 days, a total absence of growth for the residual contamination. 3.2. Effects o f t r e a t m e n t s o n e x u d a t i o n
Our results about exudation after 22 days expressed as percentages of fresh truffle weights are similar (between 15% to 20%) whatever the conditions used but less than the released amount of juice (25%) reported by Talou et al. [7] after thermal processing. Considering the juice aspect, we observed that the thermal processing led to a darker exudation juice than the high pressure processing, indicating a higher thermal damage of juice components. 3.3. Effects o f t r e a t m e n t s o n a r o m a a n d taste
Aromatic composition of fresh truffle seems not to be modified by high pressure treatments. High pressure t r e a t m e n t preserved in truffle some aromatic volatile components which were extracted in exudation liquid by heat sterilized treatment, as reported by Talou et al. [7]. After 21 days of storage at 4~ the olfactory and taste qualities of high pressurized seemed to be similar to those of heat sterilized ones, but an attractive characteristic was also found by professionnals for pressurized samples, according to the temperature used during high pressure processing.
404 Indeed, the best olfactive as well as taste evaluation was presented by samples pressurized at 40~ After the same delay in the same conditions, an attractive aroma close to that of a sterilized truffles was characterised for two pressurized samples one of which had been opened 21 days after processing. 4. CONCLUSION Results show that truffle bacteriological contamination could be reduced by high pressure processing at lower temperature than traditional sterilization. High pressure treatment (550 MPa, 30 min) could afford two types of new products according to the choosen temperature: on one hand at 40~ tasty truffles with organoleptic properties close to those of fresh truffles storable few weeks and on the other hand, at 80~ stabilized truffles closed to sterilized products but with less modified organoleptic properties. But, further investigations may be made to reduce the exudation by optimization of processing parameters (temperature, high pressure intensity, duration). It is also necessary to investigate more about high pressure effects on aromatic compounds and sensory aspect. 5. ACKNOWI~DGEMENTS Authors would like to thank the F6d6ration D6partementale des Trufficulteurs for supporting this work. 6. REFERENCES 1 2 3 4 5
6 7
R. Hayashi, R. Spiess and H. Schubert (eds.), Engineering and food, London :Applied Science, 2 (1989) 815. J.C. Cheftel, I.A.A., 108 (1991) 141. J.C. Cheftel, in C. Balny, R. Hayashi, K. Heremans and P. Masson (eds.), High Pressure and Biotechnology. J. Libbey/Eurotext, INSERM, LondonMontrouge, 224 (1992) 195. H. Kinugasa, T. Takeo, K. Fukumoto, T. Shinno and M. Ishihara, (eds.), High Pressure Bioscience and Food Science. Kyoto : Ei Pub. Co. (1993) 237. A. Suzuki, K. Kim, N. Homma,Y. Ikeuchi and M. Saito, in C. Balny, R. Hayashi, K. Heremans and P. Masson (eds.), High Pressure and Biotechnology, J. Libbey/Eurotex, INSERM, London-Montrouge, 224 (1992) 219. A. E1 Moueffak, C. Cruz, M. Antoine, M. Montury, G. Demazeau, A. Largeteau and F. Zuber, Int. J. Food Sci. Tech., 30 (1995) 391. T. Talou, M. Delmas and A. Gaset, Vitt. Flavor Fragr. J., 4 (1989) 109.