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Impact of low salt concentration, salt quality on natural large-scale sauerkraut fermentation
FOOD MICROBIOLOGY Food Microbiology 20 (2003) 391–395
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Impact of low salt concentration, salt quality on natural large-scale sauerkraut fermentation Britta Viander*,1, Maarit M.aki, Airi Palva2 MTT Agrifood Research Finland, Food Research, FIN-31600, Jokioinen, Finland Received 8 May 2002; accepted 25 October 2002
Abstract This study examined the impact of low NaCl and mineral salt concentrations on the spontaneous large-scale (430 kg) fermentation process of white cabbage into sauerkraut and sauerkraut juice. The shelf-life and sensory quality of the juices as well as the repeatability of the manufacturing process were also studied. Three parallel trials with three different salt concentrations were carried out. The NaCl concentrations in trials 1A–C and 3A–C were 0.5% and 1.2%, respectively. In trials 2A–C, we used 0.5% mineral salt (28% KCl, 57% NaCl) that gave a NaCl concentration of 0.3%. The pH decreased somewhat faster when 1.2% NaCl was used, but the lowering of pH was much the same in all cabbage containers and no significant differences could be observed after the sixth fermentation day. The growth of lactic acid bacteria in the beginning of the fermentation process was fastest in the trials where 1.2% NaCl was used and slowest in the trials with 0.5% mineral salt. With 1.2% NaCl, the number of lactic acid bacteria was 108 cfu/ml on the third fermentation day, whereas with 0.5% mineral salt the same number was reached on the sixth fermentation day and with 0.5% NaCl on the fourth fermentation day. At the end of fermentation, the lactic acid bacteria count in the pressed sauerkraut juice was 108 cfu/ml in all trials. The lactic and acetic acid concentrations were measured from juice samples during the fermentation process. Lactic acid production was clearly lower after 2 weeks fermentation in the trials where 0.5% mineral salt was used, compared to the other trials. No major difference could be detected between the acetic acid concentrations in the different trials. The sensory quality of the juices was evaluated by a trained taste panel. The sauerkraut juice fermented with 0.5% mineral salt was considered to have the best taste. We also investigated the shelf-life of the juices and found that the number of lactic acid bacteria decreased in all juices during storage at 41C. Also the number of yeasts and moulds, enterobacteria, mesophilic and thermophilic spores decreased during storage. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Sauerkraut; Sauerkraut juice; Low salt
1. Introduction The fermentation of white cabbage into sauerkraut traditionally proceeds in the presence of NaCl. The use of sodium in the production of sauerkraut has gained attention and fermentation trials have been conducted using different salt concentrations (1–3%) (Delanoe and Emard, 1971; Gangopadhyay and Mukherjee, 1971; Mayer et al., 1973; Niven, 1980). However, consumers nowadays prefer to lower their sodium intake, which has *Corresponding author. Tel.: +358-40-724-3016. E-mail addresses: britta.viander@saunalahti.fi (B. Viander), maarit.maki@mtt.fi (M. M.aki), [email protected].fi (A. Palva). 1 Putkitehtaantie 191, FIN-32270, Mets.amaa, Finland. 2 Department of Basic Veterinary Sciences, P.O. Box 57, Helsinki University, FIN-00014, Finland.
led to research work aimed at partially replacing NaCl with KCl in foods. The added concentration of NaCl in sauerkraut can, in fact, even exceed 2% (w/w). A number of studies have investigated sauerkraut containing various concentrations of NaCl, the lowest percentage of added NaCl so far being 0.6% (Pederson, 1940; Fleming and McFeeters, 1985; Trail et al., 1996). Sauerkraut has also been prepared utilizing hydrolysed protein in combination with salt at concentrations of 1.0–4.5% (Hsu et al., 1984; Wedral et al., 1985). In addition, a patent has been worked out for making sauerkraut where part of the normally added salt is replaced by an alcohol/acid mixture (Owades, 1991). Further research has focused on a reduced NaCl content in combination with lactic acid bacteria starter cultures, the used NaCl concentration being 1% (Delclos, 1992).
0740-0020/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII: S 0 7 4 0 - 0 0 2 0 ( 0 2 ) 0 0 1 5 0 - 8
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B. Viander et al. / Food Microbiology 20 (2003) 391–395
The fermented product kimchi is also traditionally produced with NaCl, but efforts have been made to replace part of the NaCl with KCl, with good results (Choi et al. 1994). In the present study, three different salt concentrations and two different types of salts were tested. The two types of salts were NaCl and mineral salt containing 28% KCl and 57% NaCl. This study focused on the impact of the variation in salt concentrations and salt quality on the natural fermentation process, as well as the repeatability of the processes. The fermentation trials were performed on a large scale at 201C. The end product was sauerkraut juice pressed from sauerkraut.
2. Materials and methods 2.1. Fermentation trials The number of natural lactic acid bacteria in the raw material was o700 cfu/100 g cabbage. Hundred gram of cabbage contained 0.41 g sucrose, 2.09 g glucose and 1.96 g fructose. The pH of the sliced cabbage was 6.5. Fermentations were carried out in plastic containers, each containing 430 kg sliced white cabbage (0.5–1 2– 3 cm2). Salt was mixed with the cabbage and the mixture was pressed tightly together and covered with a plastic film. Water was poured on the film to inhibit air from entering the cabbage mixture. According to Delanoe and Emard (1971) and Mikki and Anand (1974) the fermentation temperature was kept at 201C73. The NaCl salt was used at concentrations of 0.5% and 1.2%, while the mineral salt had a concentration of 0.5%, the percentage of NaCl being 0.3%. The used percentages of NaCl (0.3% and 0.5%) are lower than the salt percentages reported earlier in sauerkraut fermentations. The salt concentrations in trials 1A–C and 3A–C were 0.5% and 1.2%, respectively. In trials 2A–C, 0.5% mineral salt (Pansuolas, Oriola Oy Reformi-Keskus, PB 8, FIN-02101, Espoo, Finland), containing 57% sodium chloride, 28% potassium chloride, 12% magnesium sulphate, 2% lycine hydrochloride and 1% silicon dioxide was used. Each fermentation series was performed as three (A, B, C) batches to which alphabets A–C refer.
2.3. Microbiological analyses Lactic acid bacteria were enumerated by cultivation on MRS nutrition medium (Biokar Diagnostics or Difco Laboratories) containing 0.02% sodium azide and 1.5% agar for 2–3 days anaerobically at 301C. Enterobacteria were cultivated on Violet red bile agar (Biokar Diagnostics or Difco Laboratories) supplemented with 0.1% glucose and grown for 2–3 days at 371C. Mesophilic and thermophilic spores were enumerated by cultivating samples on Plate Count Agar (Difco Laboratories). The vegetative cells were destroyed by heating (801C, 10 min). Agar plates were incubated at 301C for 3 days (mesophilic spores) or at 551C for 2 days (thermophilic spores). Yeasts and moulds were grown on Yeast extract glucose chloramphenicol agar (Difco Laboratories) for 7 days at 251C. All microbiological analyses were made either in duplicate or triplicate. 2.4. Chemical analyses The pH of the cabbage juice was measured by a pHmeter (RadiometerPHM93, Radiometer Analytical) during fermentation, almost daily during the first week and after that about twice a week. Organic acids and sugars were determined by HPLC (BioRad). An Aminex HPX-87 H (BioRad) column was used with 0.009 m H2SO4 as a solvent. 2.5. Sensory evaluation A taste panel of 10 persons used in this study was trained by a professional specialist in sensory evaluations for carrying out different sensory evaluation tasks. For this study the panel was further pretrained for tasting sauerkraut juices. The juices were tasted in randomized order as blind tests. Between the samples tasted, the mouth was neutralized with water. Scoring of 1–10, where number 1 refers to not acceptable and number 10 to excellent taste and quality, was used in the evaluation. Mean values and standard deviations were calculated. The quality scale of Karlsruhe was used (Tuorila and Hellemann, 1993).
3. Results 2.2. Sampling Samples were regularly taken during the fermentation process with a specially designed perforated tube, which was laid into the sliced cabbage mixture before fermentation started. A peristaltic pump (Hiload Pump P-50, Amersham Biosciences) was used to pump the fermented cabbage juice from the containers.
To explore the effect of mineral salt and different NaCl concentrations on the quality and taste of sauerkraut juice, a large-scale sauerkraut fermentation study was carried out. In the fermentation trials where 1.2% NaCl was used (3A C), the decrease in pH was faster than in the other two fermentation trials. However, after 6 days of fermentation the pH levels were between 4 and 4.3 in
B. Viander et al. / Food Microbiology 20 (2003) 391–395
all the three trials, and no significant differences could be observed after that (Fig. 1). The concentrations of lactic and acetic acids in the cabbage juice were also measured during the fermentation process. In the trials (2A–C) with 0.5% mineral salt, the lactic acid production was clearly lower (32–46%) after 2 weeks fermentation compared to the other two trials with higher amount of salt (Fig. 2). Instead, no major difference could be observed between the acetic acid concentrations in the different trials (Fig. 2). The viable count measurements of lactic acid bacteria revealed that in the beginning of fermentation process, lactic acid bacteria grew most rapidly in the cabbage containers (3A–C) where 1.2% NaCl was added and most slowly in the cabbage containers with 0.5% mineral salt. With 1.2% NaCl, the level of lactic acid bacteria was 108 cfu/ml on the third fermentation day, whereas the same level was reached on the sixth fermentation day with 0.5% mineral salt and on the
393
fourth fermentation day when 0.5% NaCl was used. On the third fermentation day only one sample could be withdrawn from the vessels where 0.5% NaCl was used (Fig. 3). Neither mean values nor standard deviations could therefore be calculated. This data was not considered representative enough and does not give the correct number of lactic acid bacteria at this point when 0.5% NaCl was used. At the end of fermentation, the amount of lactic acid bacteria in the pressed sauerkraut juice was 108 cfu/ml in all trials. The sensory quality of the fermented sauerkraut juices was evaluated on a scale of 1–10 by a taste panel consisting of 10 trained persons. The sensory evaluation showed that the juice produced by using 0.5% mineral salt was considered to have the best taste even though the deviation of the scores was highest with this juice type (Fig. 4).
Fig. 1. Change of pH of sauerkraut during spontaneous fermentation at 201C using NaCl or mineral salt. The symbols refer to the mean values and standard deviations during pH decrease: 0.5% NaCl (K), 0.5% mineral salt (’) and 1.2% NaCl (m).
Fig. 3. Number of lactic acid bacteria in sauerkraut juices during spontaneous fermentation at 201C using NaCl or mineral salt. The bars refer to the mean values and standard deviations of bacterial colony forming units (cfu) as a function of time in three parallel cabbage vessels under three different salt concentrations. The bars with the white colour (&) refer to 0.5% NaCl, with the light grey ( ) to 0.5% mineral salt and with the dark grey ( ) to 1.2% NaCl.
Fig. 2. Concentrations of lactic acid (—) and acetic acid ( ) in sauerkraut juice during spontaneous fermentation at 201C using NaCl or mineral salt. The symbols refer to the mean values of three parallel samples and the standard deviations: 0.5% NaCl (’), 0.5% mineral salt (~) and 1.2% NaCl (m).
Fig. 4. Sensory evaluation of sauerkraut juices made with NaCl or mineral salt. The mean values and standard deviations of sensory evaluation scores for each juice type are shown as bars. The bars with the white colour (&) refer to 0.5% NaCl, with the light grey ( ) to 0.5% mineral salt and with the dark grey ( ) to 1.2% NaCl. The number of members in the test panel was 15.
B. Viander et al. / Food Microbiology 20 (2003) 391–395
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In this study, the emphasis was to evaluate the quality of sauerkraut juices, not the sauerkraut itself. It was, however, noticed that the hardness of the sauerkraut texture was dependent on the salt concentration used, being highest with the 0.5% mineral salt concentration and lowest with 1.2% NaCl. The microbiological shelflife of the fermented sauerkraut juices was also investigated. The juices were stored at 41C. Samples of the juices were taken 4, 7, 10 and 19 months after fermentation. The lactic acid bacteria counts decreased during storage in all the juices. The number of lactic acid bacteria was almost the same after 7 months of storage in all the juices, i.e. approximately 105 bacteria/ml (Table 1). The total number of yeasts and moulds varied 10-fold between the different juice types being highest (appr. 105 cfu/ml) in the juice made with mineral salt and lowest (appr. 104 cfu/ml) in the juice with 1.2% salt. During the storage the number of yeasts and moulds, however, decreased in the mineral salt juice to the same level as found with the other juices (Table 1). The total number of bacteria of the genus Enterobacteriacea was negligible in the juice with 1.2% NaCl (Table 1). In the juices with 0.5% NaCl and mineral salt the number of enterobacteria were also rather low, i.e. 100 and 400, respectively. During the storage, however, these numbers lowered further on, being after 7 months of storage approximately at the same level in all the three juice types (Table 1). The number of mesophilic and
thermophilic spores were also enumerated. The number of spores was very low and no thermophilic spores could be detected after 10 months of storage (Table 1) and no mesophilic spores after 19 months of storage (Table 1).
4. Discussion One of the main aims of this work was to study the repeatability of the production of sauerkraut juice with spontaneous fermentation of cabbages. The results obtained show clear fluctuations between parallel trials. This was probably mainly due to variations in the natural microbiota in the raw material. The original number of lactic acid bacteria on cabbage is normally very low, and the spontaneous lactic acid fermentation by which the lactic acid bacteria should finally dominate the microbial ecosystem, is a highly complex microbial process. The number of lactic acid bacteria in the cabbage raw material used was o10 cfu/g. The cabbage juice samples were taken in the same way each time during fermentation, thus ensuring that the results could be reliably compared. By taking the samples directly from the cabbage juice it was possible to make the work run more smoothly without any discernible loss in accuracy. A rapid decrease in pH in the beginning of fermentation is of great importance for the quality of the end
Table 1 Numbers of lactic acid bacteria, yeast and moulds, Enterobacteriaceae, thermophilic and mesophilic spores in sauerkraut juice stored at 41C for 19 months: 0.5% NaCl (A), 0.5% mineral salt (B) and 1.2% NaCl (C). Mean values and standard deviations of three parallel samples were calculated Time (months) 0
4
7
10
19
Lactic acid bacteria A B C
1.81 10873.50 106 2.12 10873.41 107 2.76 10871.91 108
6.97 10770.00 4.18 10770.00 13.20 10770.00
4.82 10670.00 8.42 10670.00 6.94 10670.00
26.94 10670.00 13.97 10670.00 0.10 10670.00
0.10 10570.00 0.34 10570.00 0.0070.00
Yeast and moulds A B C
63033.33721020.61 100000.0070.00 9238.0074470.58
321.0070.00 4909.0070.00 52364.0070.00
409.0070.00 15212.0070.00 606.0070.00
0.0070.00 213.3375.35 1.0570.00
0.0070.00 76.0078.66 0.0070.00
Enterobacteriaceae A B C
100.33784.30 403.337228.55 2.3371.15
27.0070.00 345.0070.00 0.0070.00
13.0070.00 26.0070.00 7.0070.00
31.0071.00 82.00714.81 9.0073.75
22.0075.62 39.00713.75 21.0075.75
Mesophilic spores A B C
— — —
37.0070.00 7.0070.00 3.0070.00
0.0070.00 0.0070.00 0.0070.00
0.0070.00 3.3370.00 0.0070.00
0.0070.00 0.0070.00 0.0070.00
Thermophilic spores A B C
— — —
0.0070.00 0.0070.00 3.0070.00
10.0070.00 7.0070.00 10.0070.00
0.0070.00 0.0070.00 0.0070.00
0.0070.00 0.0070.00 0.0070.00
B. Viander et al. / Food Microbiology 20 (2003) 391–395
product. The rapid increase in acidity minimizes the influence of spoilage bacteria. The problems usually appearing at the beginning of the sauerkraut fermentation might be minimized by the use of lactic acid bacteria starters. Reducing the influence of spoilage bacteria would most probably improve the microbiological and sensory quality of the fermented end product significantly. It is hard to achieve good repeatability in natural fermentations, and more uniform products could probably be obtained by applying starter cultures. Our results show that sauerkraut and sauerkraut juice can clearly be produced with a very low NaCl concentration as well as with a low mineral salt percentage. So far, the lowest salt content reported in commercial sauerkraut is only 0.6%, and the product is referred to as sweet sauerkraut (Fleming and McFeeters, 1985). In the present study, however, the NaCl concentration was even lower. We used a 0.5% mineral salt with only 57% NaCl, resulting in a final NaCl concentration of 0.3%. Fermentation was, however, found to be more rapid when a higher NaCl percentage was used, probably due to the capability of NaCl to extract liquid from the sliced cabbage, thereby enhancing the growth of lactic acid bacteria. Sauerkraut juice with a smoother taste was produced with mineral salt compared to the sauerkraut juices made by using ordinary NaCl. The taste panel considered this less acidic juice to be best, thereby agreeing with consumers’ preference for milder-acidflavoured sauerkraut, as reported by Fleming and McFeeters (1985). A study on commercial sauerkraut, published by Trail et al. (1996), indicates that sauerkraut manufacturers have duly paid attention to this fact. The conclusion of their report was that commercial sauerkraut nowadays contains less acidity and salt than it used to earlier. This study further indicates that fluctuations in temperature during fermentation should be avoided in large-scale production of sauerkraut juice. Particularly in the beginning of the fermentation process it is of great importance that the sliced cabbage quickly reaches the desired fermentation temperature, thereby ensuring a rapid drop in pH due to the growth of lactic acid bacteria. Due to slower pH decrease when low NaCl or low mineral salt is used the risk for contamination by spoilage microbes during fermentation is higher compared to when high NaCl is used. This will, however, probably be overcome by using lactic acid bacteria starters to ensure rapid pH decrease in the beginning of
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the fermentation process, thus minimizing the influence of spoiling microbes.
Acknowledgements The authors are grateful to Dr. Ilkka Palva for his valuable comments and advice during this study. We wish to thank Mrs. Pirjo Satka for technical assistance and Mrs. Heli V.ah.a-Touru for assistance in preparing the graphics. Furthermore, we are thankful to Arktinen Bio-Lacto Oy for participating in the fermentation trials on which this study was based. References Choi, S.-Y., Beuchat, L.R., Perkins, L.M., Nakayama, T., 1994. Fermentation and sensory characteristics of kimchi containing potassium chloride as a partial replacement for sodium chloride. Int. J. Food Microbiol. 21, 335–340. Delanoe, R., Emard, L.O., 1971. Experimental manufacture of sauerkraut in quebec. Que. Lait. Aliment. 30 (7), 11–14. Delclos, M., 1992. Vegetable preservation by a mixed organic acid fermentation. Diss. Abstr. Int. B52, 9. Fleming, H.P., McFeeters, R.F., 1985. Residual sugars and fermentation products in raw and finished commercial sauerkraut. N. Y. State Agric. Exp. St. Spec. Rep. 56, 25–29. Gangopadhyay, H., Mukherjee, S., 1971. Effect of different salt concentrations on the microflora and physico-chemical changes in sauerkraut fermentation. J. Food Sci. Technol. 8 (3), 127–131. Hsu, J.Y., Wedral, E.R., Klinker, W.J., 1984. Preparation of sauerkraut utilizing hydrolysed protein. United States Patent US4428968. Mayer, K., Pause, G., Vetsch, U., 1973. Bildung biogener amine w.ahrend der sauerkrautg.arung. Ind. Obst Gemuseverwert. . 58 (11), 307–309. Mikki, M.A., Anand, J.C., 1974. The effect of temperature on fermentation and quality of sauerkraut. Indian Food Packer 28 (5), 9–11. Niven, C.F., 1980. Technology of sodium in processed foods: general bacteriological principles, with emphasis on canned fruits and vegetables, and dairy foods. In: American Medical Association, Sodium and Potassium in Foods and Drugs, Na & K Symposium, USA, pp. 45–48. Owades, J.L., 1991. Method of making salt-free sauerkraut. United States Patent US5064662. Pederson, C.S., 1940. The relation between quality and chemical composition of canned sauerkraut. N. Y. State Agric. Exp. St. Bull. 693, 1–15. Trail, A.C., Fleming, H.P., Young, C.T., McFeeters, R.F., 1996. Chemical and sensory characterization of commercial sauerkraut. J. Food Qual. 19, 15–30. Tuorila, H., Hellemann, U., (Eds) 1993. Elintarvikkeet aistien puntarissa (Sensory Evaluation of Foods), pp. 37 and 39. University of Helsinki. Wedral, E.R., Klinker, W.J., Hsu, J.Y., 1985. Flavouring process. European Patent EP0106236B1.
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Impact of low salt concentration, salt quality on natural large-scale sauerkraut fermentation Britta Viander*,1, Maarit M.aki, Airi Palva2 MTT Agrifood Research Finland, Food Research, FIN-31600, Jokioinen, Finland Received 8 May 2002; accepted 25 October 2002
Abstract This study examined the impact of low NaCl and mineral salt concentrations on the spontaneous large-scale (430 kg) fermentation process of white cabbage into sauerkraut and sauerkraut juice. The shelf-life and sensory quality of the juices as well as the repeatability of the manufacturing process were also studied. Three parallel trials with three different salt concentrations were carried out. The NaCl concentrations in trials 1A–C and 3A–C were 0.5% and 1.2%, respectively. In trials 2A–C, we used 0.5% mineral salt (28% KCl, 57% NaCl) that gave a NaCl concentration of 0.3%. The pH decreased somewhat faster when 1.2% NaCl was used, but the lowering of pH was much the same in all cabbage containers and no significant differences could be observed after the sixth fermentation day. The growth of lactic acid bacteria in the beginning of the fermentation process was fastest in the trials where 1.2% NaCl was used and slowest in the trials with 0.5% mineral salt. With 1.2% NaCl, the number of lactic acid bacteria was 108 cfu/ml on the third fermentation day, whereas with 0.5% mineral salt the same number was reached on the sixth fermentation day and with 0.5% NaCl on the fourth fermentation day. At the end of fermentation, the lactic acid bacteria count in the pressed sauerkraut juice was 108 cfu/ml in all trials. The lactic and acetic acid concentrations were measured from juice samples during the fermentation process. Lactic acid production was clearly lower after 2 weeks fermentation in the trials where 0.5% mineral salt was used, compared to the other trials. No major difference could be detected between the acetic acid concentrations in the different trials. The sensory quality of the juices was evaluated by a trained taste panel. The sauerkraut juice fermented with 0.5% mineral salt was considered to have the best taste. We also investigated the shelf-life of the juices and found that the number of lactic acid bacteria decreased in all juices during storage at 41C. Also the number of yeasts and moulds, enterobacteria, mesophilic and thermophilic spores decreased during storage. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Sauerkraut; Sauerkraut juice; Low salt
1. Introduction The fermentation of white cabbage into sauerkraut traditionally proceeds in the presence of NaCl. The use of sodium in the production of sauerkraut has gained attention and fermentation trials have been conducted using different salt concentrations (1–3%) (Delanoe and Emard, 1971; Gangopadhyay and Mukherjee, 1971; Mayer et al., 1973; Niven, 1980). However, consumers nowadays prefer to lower their sodium intake, which has *Corresponding author. Tel.: +358-40-724-3016. E-mail addresses: britta.viander@saunalahti.fi (B. Viander), maarit.maki@mtt.fi (M. M.aki), [email protected].fi (A. Palva). 1 Putkitehtaantie 191, FIN-32270, Mets.amaa, Finland. 2 Department of Basic Veterinary Sciences, P.O. Box 57, Helsinki University, FIN-00014, Finland.
led to research work aimed at partially replacing NaCl with KCl in foods. The added concentration of NaCl in sauerkraut can, in fact, even exceed 2% (w/w). A number of studies have investigated sauerkraut containing various concentrations of NaCl, the lowest percentage of added NaCl so far being 0.6% (Pederson, 1940; Fleming and McFeeters, 1985; Trail et al., 1996). Sauerkraut has also been prepared utilizing hydrolysed protein in combination with salt at concentrations of 1.0–4.5% (Hsu et al., 1984; Wedral et al., 1985). In addition, a patent has been worked out for making sauerkraut where part of the normally added salt is replaced by an alcohol/acid mixture (Owades, 1991). Further research has focused on a reduced NaCl content in combination with lactic acid bacteria starter cultures, the used NaCl concentration being 1% (Delclos, 1992).
0740-0020/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII: S 0 7 4 0 - 0 0 2 0 ( 0 2 ) 0 0 1 5 0 - 8
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B. Viander et al. / Food Microbiology 20 (2003) 391–395
The fermented product kimchi is also traditionally produced with NaCl, but efforts have been made to replace part of the NaCl with KCl, with good results (Choi et al. 1994). In the present study, three different salt concentrations and two different types of salts were tested. The two types of salts were NaCl and mineral salt containing 28% KCl and 57% NaCl. This study focused on the impact of the variation in salt concentrations and salt quality on the natural fermentation process, as well as the repeatability of the processes. The fermentation trials were performed on a large scale at 201C. The end product was sauerkraut juice pressed from sauerkraut.
2. Materials and methods 2.1. Fermentation trials The number of natural lactic acid bacteria in the raw material was o700 cfu/100 g cabbage. Hundred gram of cabbage contained 0.41 g sucrose, 2.09 g glucose and 1.96 g fructose. The pH of the sliced cabbage was 6.5. Fermentations were carried out in plastic containers, each containing 430 kg sliced white cabbage (0.5–1 2– 3 cm2). Salt was mixed with the cabbage and the mixture was pressed tightly together and covered with a plastic film. Water was poured on the film to inhibit air from entering the cabbage mixture. According to Delanoe and Emard (1971) and Mikki and Anand (1974) the fermentation temperature was kept at 201C73. The NaCl salt was used at concentrations of 0.5% and 1.2%, while the mineral salt had a concentration of 0.5%, the percentage of NaCl being 0.3%. The used percentages of NaCl (0.3% and 0.5%) are lower than the salt percentages reported earlier in sauerkraut fermentations. The salt concentrations in trials 1A–C and 3A–C were 0.5% and 1.2%, respectively. In trials 2A–C, 0.5% mineral salt (Pansuolas, Oriola Oy Reformi-Keskus, PB 8, FIN-02101, Espoo, Finland), containing 57% sodium chloride, 28% potassium chloride, 12% magnesium sulphate, 2% lycine hydrochloride and 1% silicon dioxide was used. Each fermentation series was performed as three (A, B, C) batches to which alphabets A–C refer.
2.3. Microbiological analyses Lactic acid bacteria were enumerated by cultivation on MRS nutrition medium (Biokar Diagnostics or Difco Laboratories) containing 0.02% sodium azide and 1.5% agar for 2–3 days anaerobically at 301C. Enterobacteria were cultivated on Violet red bile agar (Biokar Diagnostics or Difco Laboratories) supplemented with 0.1% glucose and grown for 2–3 days at 371C. Mesophilic and thermophilic spores were enumerated by cultivating samples on Plate Count Agar (Difco Laboratories). The vegetative cells were destroyed by heating (801C, 10 min). Agar plates were incubated at 301C for 3 days (mesophilic spores) or at 551C for 2 days (thermophilic spores). Yeasts and moulds were grown on Yeast extract glucose chloramphenicol agar (Difco Laboratories) for 7 days at 251C. All microbiological analyses were made either in duplicate or triplicate. 2.4. Chemical analyses The pH of the cabbage juice was measured by a pHmeter (RadiometerPHM93, Radiometer Analytical) during fermentation, almost daily during the first week and after that about twice a week. Organic acids and sugars were determined by HPLC (BioRad). An Aminex HPX-87 H (BioRad) column was used with 0.009 m H2SO4 as a solvent. 2.5. Sensory evaluation A taste panel of 10 persons used in this study was trained by a professional specialist in sensory evaluations for carrying out different sensory evaluation tasks. For this study the panel was further pretrained for tasting sauerkraut juices. The juices were tasted in randomized order as blind tests. Between the samples tasted, the mouth was neutralized with water. Scoring of 1–10, where number 1 refers to not acceptable and number 10 to excellent taste and quality, was used in the evaluation. Mean values and standard deviations were calculated. The quality scale of Karlsruhe was used (Tuorila and Hellemann, 1993).
3. Results 2.2. Sampling Samples were regularly taken during the fermentation process with a specially designed perforated tube, which was laid into the sliced cabbage mixture before fermentation started. A peristaltic pump (Hiload Pump P-50, Amersham Biosciences) was used to pump the fermented cabbage juice from the containers.
To explore the effect of mineral salt and different NaCl concentrations on the quality and taste of sauerkraut juice, a large-scale sauerkraut fermentation study was carried out. In the fermentation trials where 1.2% NaCl was used (3A C), the decrease in pH was faster than in the other two fermentation trials. However, after 6 days of fermentation the pH levels were between 4 and 4.3 in
B. Viander et al. / Food Microbiology 20 (2003) 391–395
all the three trials, and no significant differences could be observed after that (Fig. 1). The concentrations of lactic and acetic acids in the cabbage juice were also measured during the fermentation process. In the trials (2A–C) with 0.5% mineral salt, the lactic acid production was clearly lower (32–46%) after 2 weeks fermentation compared to the other two trials with higher amount of salt (Fig. 2). Instead, no major difference could be observed between the acetic acid concentrations in the different trials (Fig. 2). The viable count measurements of lactic acid bacteria revealed that in the beginning of fermentation process, lactic acid bacteria grew most rapidly in the cabbage containers (3A–C) where 1.2% NaCl was added and most slowly in the cabbage containers with 0.5% mineral salt. With 1.2% NaCl, the level of lactic acid bacteria was 108 cfu/ml on the third fermentation day, whereas the same level was reached on the sixth fermentation day with 0.5% mineral salt and on the
393
fourth fermentation day when 0.5% NaCl was used. On the third fermentation day only one sample could be withdrawn from the vessels where 0.5% NaCl was used (Fig. 3). Neither mean values nor standard deviations could therefore be calculated. This data was not considered representative enough and does not give the correct number of lactic acid bacteria at this point when 0.5% NaCl was used. At the end of fermentation, the amount of lactic acid bacteria in the pressed sauerkraut juice was 108 cfu/ml in all trials. The sensory quality of the fermented sauerkraut juices was evaluated on a scale of 1–10 by a taste panel consisting of 10 trained persons. The sensory evaluation showed that the juice produced by using 0.5% mineral salt was considered to have the best taste even though the deviation of the scores was highest with this juice type (Fig. 4).
Fig. 1. Change of pH of sauerkraut during spontaneous fermentation at 201C using NaCl or mineral salt. The symbols refer to the mean values and standard deviations during pH decrease: 0.5% NaCl (K), 0.5% mineral salt (’) and 1.2% NaCl (m).
Fig. 3. Number of lactic acid bacteria in sauerkraut juices during spontaneous fermentation at 201C using NaCl or mineral salt. The bars refer to the mean values and standard deviations of bacterial colony forming units (cfu) as a function of time in three parallel cabbage vessels under three different salt concentrations. The bars with the white colour (&) refer to 0.5% NaCl, with the light grey ( ) to 0.5% mineral salt and with the dark grey ( ) to 1.2% NaCl.
Fig. 2. Concentrations of lactic acid (—) and acetic acid ( ) in sauerkraut juice during spontaneous fermentation at 201C using NaCl or mineral salt. The symbols refer to the mean values of three parallel samples and the standard deviations: 0.5% NaCl (’), 0.5% mineral salt (~) and 1.2% NaCl (m).
Fig. 4. Sensory evaluation of sauerkraut juices made with NaCl or mineral salt. The mean values and standard deviations of sensory evaluation scores for each juice type are shown as bars. The bars with the white colour (&) refer to 0.5% NaCl, with the light grey ( ) to 0.5% mineral salt and with the dark grey ( ) to 1.2% NaCl. The number of members in the test panel was 15.
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In this study, the emphasis was to evaluate the quality of sauerkraut juices, not the sauerkraut itself. It was, however, noticed that the hardness of the sauerkraut texture was dependent on the salt concentration used, being highest with the 0.5% mineral salt concentration and lowest with 1.2% NaCl. The microbiological shelflife of the fermented sauerkraut juices was also investigated. The juices were stored at 41C. Samples of the juices were taken 4, 7, 10 and 19 months after fermentation. The lactic acid bacteria counts decreased during storage in all the juices. The number of lactic acid bacteria was almost the same after 7 months of storage in all the juices, i.e. approximately 105 bacteria/ml (Table 1). The total number of yeasts and moulds varied 10-fold between the different juice types being highest (appr. 105 cfu/ml) in the juice made with mineral salt and lowest (appr. 104 cfu/ml) in the juice with 1.2% salt. During the storage the number of yeasts and moulds, however, decreased in the mineral salt juice to the same level as found with the other juices (Table 1). The total number of bacteria of the genus Enterobacteriacea was negligible in the juice with 1.2% NaCl (Table 1). In the juices with 0.5% NaCl and mineral salt the number of enterobacteria were also rather low, i.e. 100 and 400, respectively. During the storage, however, these numbers lowered further on, being after 7 months of storage approximately at the same level in all the three juice types (Table 1). The number of mesophilic and
thermophilic spores were also enumerated. The number of spores was very low and no thermophilic spores could be detected after 10 months of storage (Table 1) and no mesophilic spores after 19 months of storage (Table 1).
4. Discussion One of the main aims of this work was to study the repeatability of the production of sauerkraut juice with spontaneous fermentation of cabbages. The results obtained show clear fluctuations between parallel trials. This was probably mainly due to variations in the natural microbiota in the raw material. The original number of lactic acid bacteria on cabbage is normally very low, and the spontaneous lactic acid fermentation by which the lactic acid bacteria should finally dominate the microbial ecosystem, is a highly complex microbial process. The number of lactic acid bacteria in the cabbage raw material used was o10 cfu/g. The cabbage juice samples were taken in the same way each time during fermentation, thus ensuring that the results could be reliably compared. By taking the samples directly from the cabbage juice it was possible to make the work run more smoothly without any discernible loss in accuracy. A rapid decrease in pH in the beginning of fermentation is of great importance for the quality of the end
Table 1 Numbers of lactic acid bacteria, yeast and moulds, Enterobacteriaceae, thermophilic and mesophilic spores in sauerkraut juice stored at 41C for 19 months: 0.5% NaCl (A), 0.5% mineral salt (B) and 1.2% NaCl (C). Mean values and standard deviations of three parallel samples were calculated Time (months) 0
4
7
10
19
Lactic acid bacteria A B C
1.81 10873.50 106 2.12 10873.41 107 2.76 10871.91 108
6.97 10770.00 4.18 10770.00 13.20 10770.00
4.82 10670.00 8.42 10670.00 6.94 10670.00
26.94 10670.00 13.97 10670.00 0.10 10670.00
0.10 10570.00 0.34 10570.00 0.0070.00
Yeast and moulds A B C
63033.33721020.61 100000.0070.00 9238.0074470.58
321.0070.00 4909.0070.00 52364.0070.00
409.0070.00 15212.0070.00 606.0070.00
0.0070.00 213.3375.35 1.0570.00
0.0070.00 76.0078.66 0.0070.00
Enterobacteriaceae A B C
100.33784.30 403.337228.55 2.3371.15
27.0070.00 345.0070.00 0.0070.00
13.0070.00 26.0070.00 7.0070.00
31.0071.00 82.00714.81 9.0073.75
22.0075.62 39.00713.75 21.0075.75
Mesophilic spores A B C
— — —
37.0070.00 7.0070.00 3.0070.00
0.0070.00 0.0070.00 0.0070.00
0.0070.00 3.3370.00 0.0070.00
0.0070.00 0.0070.00 0.0070.00
Thermophilic spores A B C
— — —
0.0070.00 0.0070.00 3.0070.00
10.0070.00 7.0070.00 10.0070.00
0.0070.00 0.0070.00 0.0070.00
0.0070.00 0.0070.00 0.0070.00
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product. The rapid increase in acidity minimizes the influence of spoilage bacteria. The problems usually appearing at the beginning of the sauerkraut fermentation might be minimized by the use of lactic acid bacteria starters. Reducing the influence of spoilage bacteria would most probably improve the microbiological and sensory quality of the fermented end product significantly. It is hard to achieve good repeatability in natural fermentations, and more uniform products could probably be obtained by applying starter cultures. Our results show that sauerkraut and sauerkraut juice can clearly be produced with a very low NaCl concentration as well as with a low mineral salt percentage. So far, the lowest salt content reported in commercial sauerkraut is only 0.6%, and the product is referred to as sweet sauerkraut (Fleming and McFeeters, 1985). In the present study, however, the NaCl concentration was even lower. We used a 0.5% mineral salt with only 57% NaCl, resulting in a final NaCl concentration of 0.3%. Fermentation was, however, found to be more rapid when a higher NaCl percentage was used, probably due to the capability of NaCl to extract liquid from the sliced cabbage, thereby enhancing the growth of lactic acid bacteria. Sauerkraut juice with a smoother taste was produced with mineral salt compared to the sauerkraut juices made by using ordinary NaCl. The taste panel considered this less acidic juice to be best, thereby agreeing with consumers’ preference for milder-acidflavoured sauerkraut, as reported by Fleming and McFeeters (1985). A study on commercial sauerkraut, published by Trail et al. (1996), indicates that sauerkraut manufacturers have duly paid attention to this fact. The conclusion of their report was that commercial sauerkraut nowadays contains less acidity and salt than it used to earlier. This study further indicates that fluctuations in temperature during fermentation should be avoided in large-scale production of sauerkraut juice. Particularly in the beginning of the fermentation process it is of great importance that the sliced cabbage quickly reaches the desired fermentation temperature, thereby ensuring a rapid drop in pH due to the growth of lactic acid bacteria. Due to slower pH decrease when low NaCl or low mineral salt is used the risk for contamination by spoilage microbes during fermentation is higher compared to when high NaCl is used. This will, however, probably be overcome by using lactic acid bacteria starters to ensure rapid pH decrease in the beginning of
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the fermentation process, thus minimizing the influence of spoiling microbes.
Acknowledgements The authors are grateful to Dr. Ilkka Palva for his valuable comments and advice during this study. We wish to thank Mrs. Pirjo Satka for technical assistance and Mrs. Heli V.ah.a-Touru for assistance in preparing the graphics. Furthermore, we are thankful to Arktinen Bio-Lacto Oy for participating in the fermentation trials on which this study was based. References Choi, S.-Y., Beuchat, L.R., Perkins, L.M., Nakayama, T., 1994. Fermentation and sensory characteristics of kimchi containing potassium chloride as a partial replacement for sodium chloride. Int. J. Food Microbiol. 21, 335–340. Delanoe, R., Emard, L.O., 1971. Experimental manufacture of sauerkraut in quebec. Que. Lait. Aliment. 30 (7), 11–14. Delclos, M., 1992. Vegetable preservation by a mixed organic acid fermentation. Diss. Abstr. Int. B52, 9. Fleming, H.P., McFeeters, R.F., 1985. Residual sugars and fermentation products in raw and finished commercial sauerkraut. N. Y. State Agric. Exp. St. Spec. Rep. 56, 25–29. Gangopadhyay, H., Mukherjee, S., 1971. Effect of different salt concentrations on the microflora and physico-chemical changes in sauerkraut fermentation. J. Food Sci. Technol. 8 (3), 127–131. Hsu, J.Y., Wedral, E.R., Klinker, W.J., 1984. Preparation of sauerkraut utilizing hydrolysed protein. United States Patent US4428968. Mayer, K., Pause, G., Vetsch, U., 1973. Bildung biogener amine w.ahrend der sauerkrautg.arung. Ind. Obst Gemuseverwert. . 58 (11), 307–309. Mikki, M.A., Anand, J.C., 1974. The effect of temperature on fermentation and quality of sauerkraut. Indian Food Packer 28 (5), 9–11. Niven, C.F., 1980. Technology of sodium in processed foods: general bacteriological principles, with emphasis on canned fruits and vegetables, and dairy foods. In: American Medical Association, Sodium and Potassium in Foods and Drugs, Na & K Symposium, USA, pp. 45–48. Owades, J.L., 1991. Method of making salt-free sauerkraut. United States Patent US5064662. Pederson, C.S., 1940. The relation between quality and chemical composition of canned sauerkraut. N. Y. State Agric. Exp. St. Bull. 693, 1–15. Trail, A.C., Fleming, H.P., Young, C.T., McFeeters, R.F., 1996. Chemical and sensory characterization of commercial sauerkraut. J. Food Qual. 19, 15–30. Tuorila, H., Hellemann, U., (Eds) 1993. Elintarvikkeet aistien puntarissa (Sensory Evaluation of Foods), pp. 37 and 39. University of Helsinki. Wedral, E.R., Klinker, W.J., Hsu, J.Y., 1985. Flavouring process. European Patent EP0106236B1.