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

Target use: Research and Quality Control of processing and preservation methods used for fresh cut fruits and vegetables.

Introduction

신선한 과일과 채소는 특히 방부제가 거의 없는 신선한 제품으로 소비자들에게 제공되기 때문에 부패하기 쉬운 경향이 있습니다. 절단, 파쇄 또는 박리와 같은 공정은 변색, 갈변 및 질감 또는 맛의 변화가 일어나기 때문에 소비자들의 변심이 생길수 있습니다. 기계적 변형에 의한 상처로 소비자들의 변심이 높은 비율로 나타날수 있고 이는 부패성과 관련있는 것으로 알려져있습니다[1}. 이 호흡 속도는 등온 열량측정 곡선에서 쉽게 볼 수 있습니다. Calmetrix Biocal과 같은 등온열량 측정기에서는 절단, 박피 또는 파쇄로 인한 다양한 유형의 상처에 의한 효과 뿐만 아니라 처리방법에 의한 부패를 최소화하기 위해 호흡 속도에 대한 특정 보관 조건, 온도 및 다른 가능한 보존 방법을 연구 할 수 있습니다.

결과는 기술자의 외부 개입없이 지속적으로 측정할 수 있고 실험 종료시 쉽게 검색하고 분석할 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 플라스틱이나 스테인리스 스틸 엠플을 사용하는 Biocal과 같은 큰 샘플셀 을 이용하는 열량계를 사용하면  과일과 채소 혹은 다른 모양과 크기로 잘린 과일과 채소 그리고 식품과 같이 연구할 수 있는 식품의 범위가 늘어날 것입니다.

이 Application Note는 무화과, 과일 전체나 조각 모두에서 발생하는 호흡으로부터 열 변화를 보여줍니다.

Test Protocol

In a Biocal 2000 calorimeter at 23 °C,  one  sample  channel  contained a whole fresh fig (37.5 g), while the other channel  contained a similar fresh fig (34.5 g) cut in 10 mm pieces.

Results and Interpretation

Both  samples  show  similar  respiration  at  about  0.2  mW  for  about 15 h. After this, the heat production from the cut fruit  starts  to  increase  in  an  “exponential”  way.  When  the  vials  were  opened  after  the  experiment,  the  cut  fig  was  heavily  molded.

The  rate  of  respiration  of  0.2  mW  for  a  fruit  with  a  mass  of about 35 g, corresponds to about 6 µW/g fresh mass.

The microbiological activity shows – as it commonly does – an  accelerating  phase.  This  is  usually  termed  the  “exponential”  phase,  but  perfectly  exponential  behavior  is  mainly  seen  in  liquid cultures. In the present case we have surface growth of  molds (and possibly also other organisms, e.g., bacteria), and  the rate of such a process is not only influenced by how fast  the  organism  can  grow,  but  also  by  such  factors  as  nutrient availability and crowding on the surface.

Both  figs  and  molds  are  aerobic  organisms:  in  contrast  to  yeast  and  many  bacteria,  they  need  oxygen  for  their  metabolism.  If  we  assume  that  all  the  measured  heat  comes  from aerobic metabolism (respiration) we can calculate how  much oxygen is consumed during the experiment, as the heat  or respiration is known to be about -455 kJ/mol (O₂) [2]. The  whole fig produces about 20 J during the measurement; this  corresponds to 44 µmol of consumed oxygen. For the cut fig  the total heat is about 35 J, corresponding to about 77 µmol  oxygen. Both these amounts of oxygen are quite low; the air in  a  125  mL  ampoule  with  a  fig  can  support  respiration  producing about 400 J of heat. It is important to not run out of  oxygen  in  respiration  experiments,  but  in  this  case  the  respiration is very low, so that the oxygen level only dropped  from 21% to about 20% during the measurement.

Conclusion

Isothermal calorimeters such as Biocal 2000 and Biocal 4000  are  an  effective  and  easyItoIuse  tool  to  measure  respiration  rate  due  to  wounding  of  fresh  fruits  and  vegetables.  The  method  described  in  this  Application  Note  can  be  used  for  example for small whole fruit, as well as fresh-cut produce in  general and to study the metabolic response to various cutting  or peeling methods.

References

1. Bolin, H.R. and Huxsoll, Effect of preparation and storage  parameters on quality retention of salad-cut lettuce. Journal of  Food and Science 5691(1991) 60-67.
    
2. Hansen,  L.  D.,  C.  MacFarlane,  et  al.  (2004).  "Use  of  calorespirometric  ratios,  heat  per  CO₂  and  heat  per  O₂,  to  quantify  metabolic  paths  and  energetics  of  growing  cells."  Thermochim Acta 422: 55-61.
    
3. Wadsö,  L.  and  F.  Gómez  Galindo  (2009).  "Isothermal  calorimetry  for  biological  applications  in  food  science  and  technology." Food Control 20(10): 956-961.