Instruments to which this note applies:  Biocal 2000, Biocal 4000 

Target use: Research and Quality Control related to fermentation of foods including dairy products, beer, wine and spirits and other fermentation processes.

Introduction 

발효는 선사시대부터 보존이나 맛을 위해 탄수화물이 풍부한 고형 식품이나 액체를 처리하는데 사용되었습니다. 발효는 등온 전도 열량계로 연속적으로 측정하기 쉬운 유기산, 알코올 및 가스의 조합물을 생성할 수 있습니다.

발효의 효과는 균주의 선택, 농도, 온도 등과 같은 요인에 의해 결정됩니다. 이러한 요인들에 의한 발효반응의 효과는 등온열량 곡선에서 매우 잘보이고 외부 요인없이 모니터링 할 수 있습니다. 결과는 버튼클릭으로 검색할 수 있습니다. 이것은 등온열량측정법이 다른 식품에 발효가 어떻게 진행되는지 평가할 수 있는 편리하고 효과적인 도구가 되며, 단순히 등온열량측정 곡선을 비교하여 온도, 스타터 농도 등의 함수로 발효 속도를 쉽고 빠르게 비교할수 있습니다. 125ml 샘플 바이알를 사용하는 Calmetrix Biocal과 같이 큰 샘플 세포 열량계를 이용한다면 채소, 육류 또는 치즈 그리고 다른 고형 그리고 액체 식품과 같이 연구할 수 있는 식품의 범위가 늘어날 것입니다.

이 Application Note는 23 °C에서 2종류의 다른 스타터 배양으로 처라한 저온살균 우유샘플에서의 열량변화를 보여준다.

Test Protocol

A small amount of starter culture (the fermented product) was  added to milk, mixed and loaded into 125 ml sample vials that  were placed in the calorimeter. The two samples only differed  in  the  concentration  of  starter  culture  that  was  used  (0.2%  and 1% by mass of fermented product.

Results and Interpretation

Both  samples  show  the  typical  behavior  during  milk  fermentation.  First  one  exponential  phase  that  ends  with  a  sudden  drop  in  activity,  then  the  second  main phase.  The sample with lower starter concentration is slower.

The sample with less culture lags about 3 h behind the other  sample as the microorganisms with lower initial concentration   take  longer  time  to  multiply  to  reach  a  certain  number  of  bacteria (and a certain thermal power). As the ratio between  the initial concentrations was 5 and it took 3 h for the lower   concentration  to  reach  the  level  of  the  higher  one,  the  time  constant of the exponential growth can be inferred easily from  solving the equations for exponential growth:

            
This  corresponds  to  a  doubling  time  of  about  1.3  h,  i.e.,  the  bacteria divide every 1.3 h.

Conclusion

Isothermal calorimeters such as Calmetrix’s Biocal models are  an effective and easy-to-use tool for the study of fermentation  processes, especially such processes for which it is difficult to  follow  the  reaction  with  pH-sensors,  like  non-acidifying  cultures or solid foodstuffs. One example of such applications  is to study the effectiveness of  starter cultures, as shown in  this  Note.  After  only  a  few  hours,  or  even  earlier  at  higher  concentration,  the  activity  of  the  starter  culture  can  be  measured effectively through a simple visual interpretation of   the  calorimetry  graph.  A  closely  related  use  may  also  be  to  check the content of active microorganisms in pro-biotic foods.

References

1. Stulova,  I.,  et  al.,  Fermentation  of  reconstituted  milk  by  Streptococcus*thermophilus: Effect of irradiation on skim milk  powder. Int. Dairy J., 31 (2013) 139-149
    
2. Wadsö, L. and F. Gómez Galindo, "Isothermal calorimetry for biological  applications  in  food  science  and  technology."  Food Control 20(10) (2009)  956-961.
    
3. Riva,  M.,  et  al.,  Growth  and  fermentation  activity  of  Streptococcus* thermophilus  and  Lactobacillus* bulgaricus  in  milk: a calorimetric investigation.  Annali  di  Microbiologia  ed  Enzimologia, 47 (1997) 199-211 (in English).