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Food Control 41 (2014) 122e127

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Food Control

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Starter culture fermentation of Chinese sauerkraut: Growth,acidification and metabolic analyses

Tao Xiong a,b,*, Xiao Li a,b, Qianqian Guan a,b, Fei Peng a,b, Mingyong Xie a

a State Key Laboratory of Food Science & Technology, No. 235 Nanjing East Road, Nanchang, Jiangxi, 330047, PR ChinabCollege of Life Science & Food Engineering, Nanchang University, No. 235 Nanjing East Road, Nanchang, Jiangxi, 330047, PR China

a r t i c l e i n f o

Article history:Received 28 August 2013Received in revised form17 December 2013Accepted 31 December 2013

Keywords:Chinese sauerkrautStarter culture fermentationLactic acid bacteriaMetabolism

* Corresponding author. State Key Laboratory of Fo235 Nanjing East Road, Nanchang, Jiangxi, 330047, PRTel.: þ86 13697084048; fax: þ86 791 3063627.

E-mail address: xiongtao0907@163.com (T. Xiong)

0956-7135/$ e see front matter � 2014 Elsevier Ltd.http://dx.doi.org/10.1016/j.foodcont.2013.12.033

a b s t r a c t

Chinese sauerkraut is a kind of traditional and typical fermented food. Four lactic acid bacteria (LAB)strains, Leuconostoc mesenteroides NCU1426, Lactococcus lactis NCU1315, Lactobacillus plantarumNCU1121 and Lactobacillus casei NCU1222 isolated from Chinese sauerkraut, were used in single startercultures. Microbiological changes and pH values were monitored during fermentation. Metabolic sub-strates and products during the fermentation were examined using high performance liquid chroma-tography (HPLC) technology. Results have shown that Leu. mesenteroides and Lc. lactis grew faster,produced lactic acid earlier and were poorly acid-resistant, whereas Lb. plantarum and Lb. casei producedmuch more lactic acid throughout fermentation and showed better acid-tolerance. Two Lactococcus hadoutstanding performance in sucrose utilization while the other two Lactobacillus were likely to useglucose and fructose during fermentation. Unexpectedly, Leu. mesenteroides and Lc. lactis showed weakcitric acid metabolism in fermentation. All the four LAB strains were able to utilize malic acid in earlyfermentation. In conclusion, these LAB strains have shown notable differences in growth and fermen-tative properties during starter culture fermentation of Chinese sauerkraut, probably resulting from LABfermentative function and a mixture of complex substrates.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Chinese sauerkraut is a traditional fermented vegetable foodwhich is widely consumed in many regions of China. To produceChinese sauerkraut, various vegetables, such as cabbage,radish, tender ginger and pepper, are pretreated and thenimmersed in 6e8% (w/v) salt solution blended with various in-gredients like garlic and Illicium verum, and then left at ambienttemperature (20e25 �C) for 6e10 days in pickle jars, allowingfermentation to proceed. Unlike kimchi which uses direct salting towithdraw juice from the cabbage (dry salting), Chinese sauerkrautis a type of brine-salted and lactic acid fermented vegetable product(Yan, Xue, Tan, Zhang, & Chang, 2008). Lactic acid bacteria (LAB) areimportant in many food fermentations because they contribute tosensory characteristics and preservative effects (Holzapfel, 1995)with their physiological features such as substrate utilization,metabolic capabilities and probiotic properties. Some of the LAB are

od Science & Technology, No.China.

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homofermentative, and produce lactic acid as the main product ofglucose fermentation, while others are heterofermentative andproduce carbon dioxide and ethanol in addition to lactic acid(Blandino, Al-Aseeri, Pandiella, Cantero, & Webb, 2003). The maingroups of LAB include Lactobacillus, Leuconostoc, Pediococcus andStreptococcus. Our previous study has shown that Lactococcus lactissubsp. lactis, Leuconostoc mesenteroides subsp. mesenteroides,Lactobacillus plantarum and Lactobacillus casei dominated the nat-ural fermentation of Chinese sauerkraut, and Leuconostoc mesen-teroideswas categorized as heterofermentative LAB while the otherthree strains as homofermentative LAB (Xiong, Guan, Song, Hao, &Xie, 2012).

LAB are widely used as starter culture in the production of fer-mented foods (Knorr, 1998) and vary in their functional properties.The use of one starter culture was reported to help standardize thefermentation by controlling the microbial flora (Font de Valdez, DeGiori, Garro, Mozzi, & Oliver, 1990). It was reported that organicacids and volatile organic compounds were produced duringtraditional and starter culture fermentation of Bushera, a Ugandanfermented cereal beverage (Muyanja, Narvhus, & Langsrud, 2012).Albert Hurtado, Reguant, Bordons, and Rozès (2010) evaluated thepotential of the strain Lactobacillus pentosus as a starter duringArbequina table olive fermentation, in which both the LAB strain

Fig. 1. Changes in the counts of four experimental LAB strains during starter culturefermentation of Chinese sauerkraut. Results are means of four independent trials(n ¼ 4). Error bars represent the standard deviation.

T. Xiong et al. / Food Control 41 (2014) 122e127 123

and organic acids were monitored. Some LAB including Leu. mes-enteroides, Leu. citreum and Lb. plantarum have been suggested asstarter cultures for quality development in vegetable fermentation(Chang & Chang, 2010; Giraffa, 2004; Johanningsmeier, McFeeters,Fleming, & Thompson, 2007; Leal-Sánchez et al., 2003; Wiander &Ryhänen, 2005). Jung et al. (2012) investigated the effects of a Leu.mesenteroides strain as a starter culture for kimchi fermentation byanalyzing kimchi microbial succession and metabolites. In fact, thestarter culture of LAB in fermentation of cucumbers, cabbage andother products has been used for several decades. Nevertheless,pure cultures are presently used only on a limited commercial scalefor these commodities. To the best of our knowledge, previousstudies regarding the starter culture fermentation of Chinesesauerkraut mainly focused on nitrite depletion caused by inocu-lating LAB starter cultures, and on comparison analysis of aromacompounds between natural and starter culture fermentation.However, there is little information on the study target to popu-lation change and analyses on substrates and products duringstarter culture fermentation using different LAB strains isolatedfrom Chinese sauerkraut, which is a basis for assessing thefermentative properties of these LAB strains and development ofsuitable starter cultures.

The major objective of this study was to assess the LAB strainspreviously isolated from Chinese sauerkraut as single starter cul-tures for their fermentative properties. Microbiological changesand physicochemical characteristics were monitored duringfermentation. Substrates utilization and metabolites formationwere analyzed by detection of sugars and organic acids using highperformance liquid chromatography (HPLC) technology. As far aswe know, we have for the first time studied starter culture fer-mented Chinese sauerkraut from the perspective of substrates andmetabolism.

2. Materials and methods

2.1. Materials

Fresh cabbage and other ingredients used in fermentation werepurchased from local supermarkets in Nanchang, Jiangxi Province,China.

2.2. Starter culture preparation

Four pure LAB strains, Leuconostoc mesenteroides NCU1426,Lactococcus lactis NCU1315, L. plantarum NCU1121 and L. caseiNCU1222 were used in Chinese sauerkraut fermentation underlaboratory controlled conditions. Cells of each LAB strain werecultured in MRS broth at 30 �C for 18 h to reach a concentration of109 cfu/mL. Cells were harvested by collecting cell pellets aftercentrifuging 50 ml of each culture at 4500 rpm for 10 min. The cellpellets were washed twice with saline and resuspended in 0.9%saline to produce LAB suspensions of approximately 106 cfu/mL forstarter inoculation.

2.3. Preparation of sauerkraut and sampling

Cabbages were washed, dried, cut into small pieces and put into5 L pickle jars along with spices, including garlic (3%), Chineseprickly ash (1.5%), red peppers (3%) and ginger (2%). In this study,1000 g cabbages were used for each starter culture fermentation.Pickle jars filled with thematerials were then sterilized at 105 �C for15min. Cool sterile 2000ml water containing 6% salt and 3% crystalsugar was then added into the cool pickle jar. For fermentationusing starter cultures, 0.1% (v/v) of cell suspension (106 cfu/mL) ofeach LAB strain was inoculated. The jar was sealed with water to

exclude air, and then kept at ambient temperature (20e25 �C) for 7days. Four jars were made and monitored for each LAB strain(n ¼ 4). During the fermentation, brine was sampled asepticallyevery 12 h and divided into two portions. One portion was used foranalysis of LAB flora and measurements of pH value and the otherportion was stored at �20 �C for HPLC analysis.

2.4. Enumeration of LAB

LAB growth was monitored by enumeration on MRS agar (DeMan, Rogosa, & Elisabeth Sharpe, 1960. Colony-forming units[CFU]/mL). A 10 ml brine sample was homogenized in 90 ml sterilesaline solution (0.85%, w/v). Appropriate dilutions were made and0.1 ml of the appropriate decimal dilutions were plated onto theMRS agar and incubated anaerobically at 37 �C for 48 h, and thenthe plate counts were obtained.

2.5. Determination of pH value, sugar and organic acids

The pH of the brine samples was determined using a pH meter,calibrated using standard buffer solutions at pH 4.0 and 6.8. Theconcentrations of sugars (sucrose, glucose and fructose) andorganic acids (lactic, acetic, citric and malic acids) were determinedusing high performance liquid chromatography (HPLC, Agilent,USA) equipped with a manumotive injector, a 1260 Quat pump anda 1260 column heater (Agilent, USA). A 1260 variable wavelengthUV detector and a refractive index detector (Agilent, USA) wereused for determination of sugars and organic acids, respectively. AnAminex HPX-87H column (300 � 7.8 mm, Bio-Rad) held at 45 �C,using 6 mM H2SO4 as a mobile phase at a flow rate of 0.5 ml/minwas used for the separation of sugars and organic acids. Thedetected wavelength of the UV detector for organic acids was205 nm. Samples (1 ml) were unfreezed and centrifuged(12,000 rpm,10min), then supernatant was filtered through a 0.22-mm filter, and 20 mL of which was injected into the chromatograph.The sugars and organic acids were identified and quantified bycomparison of their retention times and peak areas with standards.

2.6. Statistical analyses

Data are given as mean values (n ¼ 4) accompanied by thestandard errors of means. Analyses of variance (ANOVA) was per-formed on the data obtained every 12 h, followed by Student’s t-

T. Xiong et al. / Food Control 41 (2014) 122e127124

test using SPSS 13.0. Differences were considered significant atp < 0.05.

3. Results and discussion

3.1. Microbiological changes during fermentation

As shown in Fig. 1, the largest increase in counts of Leu. mes-enteroides and Lc. lactis was observed during the first 24 hfermentation, and then the growth reached a stationary phase. Anoteworthy decrease was seen in the third day, followed by acontinuous reduction until the end of fermentation. Comparedwith the two Lactococcus, two Lactobacillus grew more slowlyduring the first day. Lb. plantarum, and Lb. casei reached stationaryphase after 1.5 days and 2.5 days, respectively. Unlike Leu. mesen-teroides and Lc. lactis, populations of these two Lactobacillus strainsconsistently kept at the high levels and decreased slightly in the 7thday.

It was reported that Leu. mesenteroides predominated the earlystage and Lb. plantarum terminated the fermentation in sauerkrautfermentation (Pederson & Albury, 1969). The starter culturefermentation in the present study was consistent with this report.The rapid growth of Leu. mesenteroides may benefit from its het-erofermentative pathway in sugar utilization. As the pH decreased,Lactococcus and Lactobacillus showed significant difference(P< 0.01) in population decline, whichmay be due to the differencein acid-tolerance.

3.2. Changes in pH value during fermentation

Throughout fermentation, the mean pH value of Leu. mesenter-oides and Lc. lactis starter fermentations declined from 5.40 to 5.30to 3.50 and 3.45 (Fig. 2), respectively, whereas from 5.32 to 5.52 to3.10 and 3.20 in starter fermentations with Lb. plantarum and Lb.casei. Noteworthy differences in pH value decline were seen duringthe first 1.5 day fermentation. In the Leu. mesenteroides and Lc. lactisstarter fermentations, pH value decreased rapidly in the first day,followed by a slow reduction. In contrast, Lb. plantarum and Lb. caseishowed much tardier pH value drop during the first day, and thefastest drop in pH was observed in the second day.

Significant difference (p < 0.05) in pH value decrease amongstrains was observed. Leu. mesenteroides and Lc. lactis gave fasteracidification at early stage than Lb. plantarum and Lb. casei did.However, Lb. plantarum and Lb. casei showed greater acidification

Fig. 2. pH changes in the brines during starter culture fermentation of Chinesesauerkraut (n ¼ 4).

throughout the whole fermentation. Different fermentation typesand acid-tolerance of strains may be responsible for these results.Particularly, Lc. lactis, also as a homofermentative LAB, showed alimited acid-producing capacity and poorer acid-tolerance, whichwas similar to the finding by Tolonen et al. (2004).

3.3. Changes in levels of sugars and organic acids duringfermentation

The changes in concentrations of sugars (sucrose, glucose andfructose) and organic acids (lactic, acetic, citric and malic acid)during starter culture fermentation were shown in Fig. 3(AeG). Asmentioned above, crystal sugar, mainly containing sucrose as wellas a certain amount of glucose and fructose (Data not shown), wasused in fermentation as additive. The composition of the raw cab-bage (juice) was also detected and summarized in Table 1. Glucoseand fructose constituted most of the fermentable sugars in thecabbage juice, while sucrose only accounted for a small fraction. Inaddition, citric and malic acid present in the cabbage can diffuseinto the brine and are then depleted. As shown in Fig. 3-A, sucrosewas utilized throughout each fermentation to varying degrees. Thegreatest decrease of sucrose was observed in fermentation by Leu.mesenteroides, followed by Lc. lactis, indicating a better sucroseutilizing capacity of the Lactococcus, especially the hetero-fermentative Leu. mesenteroides. In comparison, two Lactobacillusutilized much less sucrose during fermentation. In all starter cul-ture fermentation, glucose concentration increased rapidly in thefirst 0.5 day and then sharply decreased in the following day. Afterthat, small declines continued till the end of the fermentation bythe two Lactobacillus. However, little increases of glucose wereobserved in the fermentations by Leu. mesenteroides and Lc. lac-tis(Fig. 3-B). Fructose increased at the early stage and thendecreased to a low level in fermentations by Lb. plantarum and Lb.casei. Leu. mesenteroides and Lc. lactis showed significant increasesin fructose within the first 2 days and with a slight increasethereafter (Fig. 3-C). Citric acid concentration increased and thenplateaued in fermentation inoculated with Leu. mesenteroides andLc. lactis, indicating weak citric acid utilization by these two strains.With respect to Lb. plantarum and Lb. casei, the concentration ofcitric acid initially increased, then dramatically declined, and keptstable finally (Fig. 3-D). Malic acid wasmetabolized at early stage bythese four strains (Fig. 3-E). During each starter fermentation malicacid concentration increased in the first 0.5 day and then rapidlydecreased in the following 0.5e1 day to a nearly stable level. Due tothe utilization of fermentable substrates and the population in-crease of the LAB, lactic acid, the main acid product in Chinesesauerkraut fermentation, notably increased. There was a significantdifference (p < 0.01) in final lactic acid concentration between theLactococcus and Lactobacillus starters (Fig. 3-F). HomofermentativeLAB produced far more lactic acid during fermentation, with theexception of Lc. lactis. Compared with the Lactobacillus, Leu. mes-enteroides and Lc. lactis did not show continuous increase in lacticacid after 2.5 days. In addition, these two strains produced almostthe same amount of acetic acid during fermentation, which weresignificantly (p < 0.01) higher than that produced by Lb. plantarumand Lb. casei (Fig. 3-G). In fact, Lb. casei almost did not produceacetic acid.

It was found that these four selected LAB strains varied in sub-strate utilization and product formation during Chinese sauerkrautfermentation. Glucose, fructose, citric acid andmalic acid, known asthe fermentable substrate, diffused from the cabbage as soon as thefermentation started, which could explain their increase in the first0.5 day fermentation. Also, the diffusion of these two organic acidscontributed to the slight drop of pH value in early hours. As atraditional manufacture method, crystal sugar was added in the

Fig. 3. Sugar and organic acid concentration changes in the brines during starter culture fermentation of Chinese sauerkraut (n ¼ 4). The A, B, C, D, E, F and G represents sucrose,glucose, fructose, citric acid, malic acid, lactic acid and acetic acid, respectively.

T. Xiong et al. / Food Control 41 (2014) 122e127 125

Table 1Sugar and organic acid concentrations in cabbage juice (n ¼ 4).

Composition Sucrose Glucose Fructose Lactic acid Acetic acid Citric acid Malic acid

Concentration (mM) 1.65 � 0.21 74.82 � 5.15 19.42 � 2.07 0.00 10.60 � 1.68 7.94 � 0.91 14.36 � 1.72

T. Xiong et al. / Food Control 41 (2014) 122e127126

Chinese sauerkraut fermentation, which makes a complex sugarconstitution. Sucrose as the major sugar could be directly metab-olized or hydrolyzed by sucrose hydrolase forming equimolaramount of glucose and fructose. The Lactococcus strains, especiallythe Leu. mesenteroides, had much more sucrose consumption,which could be ascribed to high constitutive levels of specific per-meases and/or hydrolyzing enzymes (Gonzalez & Kunka, 1986;Mital, Shallenberger, & Steinkraus, 1973). Furthermore, sucrosewas found to be a better sugar to be utilized than fructose orglucose for Leuconostoc. species, suggesting its rapid growth byconsuming sucrose during the early stage of fermentation (Cho,Lee, Jeon, Kim, & Han, 2006; Dols, Chraii, Remaud-Simeon, Lind-ley, & Monsan, 1997). It is noteworthy that certain amount of su-crose could diffuse into cabbage mesophyll from brine, which alsocaused the consumption of sucrose. Hexose fermentation is themost common in lactic acid bacteria, and hexose, especially glucose,is normally regarded as the optimal fermentable sugar to most ofLAB. In our study, Lb. plantarum and Lb. casei showed significantly(p < 0.05) greater reduction in glucose and fructose consumption,verifying a preference in sugar utilization. To heterofermentativeLAB, fructose is catabolized by the heterolactic pathway but canalso be transformed into mannitol by mannitol dehydrogenase, acollateral reactionwhere NAD(P)H is regenerated (Veiga-da-Cunha,Santos, & Van Schaftingen,1993). However, a significant decrease offructose was not observed in Leu. mesenteroides starter fermenta-tion, which may be attributed to the high concentration of sucrose.

It was known that there were two major pathways of hexosefermentation occurring within LAB in vegetable fermentation.Homofermentative LAB produce lactic acid as the major or soleend-product via Embden-Meyerhof-Parnas pathway, whereasheterofermentative LAB use 6P-gluconate pathway to generateequimolar amount of lactic acid, CO2 and acetic acid or ethanol. Inthis study, Leu. mesenteroides, Lb. plantarum and Lb. casei showedsignificant difference in hexose uptake as well as lactic acid andacetic acid production which is consistent with their respectivefermentation types. Moreover, Lb. plantarum showed the best acid-producing capacity compared with other strains. Interestingly, Lc.lactis, as a homofermentative LAB, showed similarities in sugaruptake and organic acids formation to Leu. mesenteroides ratherthan the two Lactobacillus. These results suggest that the fermen-tation types cannot be distinguished by the fermentation end-products if complex substrates are fermented containing com-pounds other than hexoses.

Many LAB use citrate as substrate (electron acceptor) for co-metabolism with sugars like glucose, fructose, lactose, or xyloseproviding NADH (citrateþ2 [H] / lactate þ acetate þ CO2) (Hacheet al., 1999; Salou, Loubiere, & Pareilleux, 1994; Schmitt et al., 1997;Starrenburg & Hugenholtz, 1991). Citrate metabolism is reportedimportant in Lc. lactis and Leu. mesenteroides strains which are oftenused in the dairy industry. However, Leu. mesenteroides and Lc. lacisin the present study did not show citrate decrease duringfermentation probably due to the complex mixture of substrates.

It has been reported that some LAB had the ability to decar-boxylate L-malic acid to L-lactic acid and CO2 with a malolacticenzyme (Kunkee, 1967; Radler, 1986). Since malic acid is a majororganic acid in cabbage, reduction of malic acid is likely to occurduring fermentation. Our results suggested that four LAB strainswere able to produce a malolactic enzyme and metabolize malic

acid in fermentation, which has potential for influencing the rate ofpH decrease at early stage.

4. Conclusions

In our study, we studied the substrates composition of Chinesesauerkraut as well as the substrate utilization and metabolicproducts of the four selected LAB during fermentation. Growth andmetabolic activities vary among the four experimental strainsduring starter culture fermentation of Chinese sauerkraut. Leu.mesenteroides NCU1426 and Lc. lactis NCU1315 utilized sucrosebetter and showed earlier rapid growth, whereas Lb. plantarumNCU1121 and Lb. caseiNCU1222 seemed to prefer using glucose andfructose and showed greater acid-tolerance at low pH values. All ofthe four strains were able to metabolize malic acid in earlyfermentation stage. Both Leu. mesenteroides NCU1426 and Lc. lactisNCU1315 showed weak utilization in citric acid, which was notconsistent with the previous studies. Lb. plantarum NCU1121 andLb. casei NCU1222 possessed better acid-producing abilities thanthe other two strains. A complex mixture of fermentable substrateswith a high concentration of sucrose exist in Chinese sauerkrautfermentation, during which some metabolic activities of the LABmay be affected. However, the effects of substrate composition andconcentration on the microbial community and metabolite pro-duction during Chinese sauerkraut fermentation have not yet beenreported. Further studies on monitoring the activities of typicalenzymes related to LAB metabolism during fermentation arerequired.

Acknowledgments

The financial supports from the National Natural ScienceFoundation of China (NSFC, Project No. 31060224) and the NationalHigh Technology Research and Development Key Program of China(863 Key Program, 2011AA100904) and State Key Laboratory ofFood Science and Technology, Nanchang University (Project No.SKLF-ZZB-201309 and No. SKLF-ZZA-201303 and No. SKLF-KF-201210) are gratefully acknowledged.

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