Thursday, May 16, 2024

Test drying with food dehydrator

 Samples: lysate of dry yeast #1(Allinson)

Food dehydrator, 68oC, 24 hours

Observation: darken, stick to container

-->Dissolve in water and dry using freeze dryer, ~30 hours
Can be broken down easily to pieces or powder.

To test food dehydrator at 60oC for different durations.

Friday, April 19, 2024

Bitterness of yeast extracts

 


The bitterness of yeast extract primarily arises from various compounds produced during the breakdown of yeast cells. These include:


Nucleotides and Nucleosides: When yeast cells are broken down, nucleotides such as guanosine monophosphate (GMP) and inosine monophosphate (IMP), and nucleosides like guanosine and inosine, are released. These compounds have inherent bitter tastes.


Amino Acids: Certain amino acids, particularly hydrophobic ones like leucine, isoleucine, and phenylalanine, contribute to the bitter taste in yeast extract. The concentration and presence of these amino acids can significantly influence the overall bitterness.


Peptides: During the breakdown of proteins in yeast cells, peptides are formed. Some of these peptides, especially those containing hydrophobic amino acids, have a bitter taste.


Maillard Reaction Products: The Maillard reaction, which occurs during the heating process of yeast extract production, can also produce bitter compounds. This reaction typically involves reducing sugars and amino acids that form complex molecules contributing to flavor and, sometimes, bitterness.


Other Organic Compounds: Other organic compounds produced during yeast autolysis, such as certain esters and alcohols, might also contribute to the bitterness, although their impact is usually less pronounced compared to nucleotides and amino acids.


Understanding these components helps in adjusting the production processes of yeast extract to manage and potentially reduce its bitterness, making it more palatable for various applications in food products.


User

Suggest autolysis conditions that would minimize bitterness of the yeast extract

ChatGPT

Minimizing the bitterness of yeast extract through optimal autolysis conditions involves careful control of several parameters during the yeast breakdown process. Here are some suggestions for adjusting autolysis conditions to reduce bitterness:


1. Temperature Control

Optimal Temperature: Conducting autolysis at a lower temperature can help minimize the activity of enzymes that produce bitter compounds. Generally, temperatures around 45-50°C are recommended. Higher temperatures can accelerate the breakdown process but may lead to increased bitterness due to enhanced enzymatic activity.

2. pH Adjustment

Optimal pH: Maintaining a slightly acidic to neutral pH during autolysis can help control the enzymatic activity that leads to bitterness. A pH range of 5.5 to 6.5 is often effective. Adjusting the pH with food-grade acids such as citric acid can help manage enzymatic reactions during autolysis.

3. Enzyme Control

Enzyme Inhibitors: Using specific enzyme inhibitors can prevent the formation of bitter peptides. For instance, protease inhibitors can be added to the autolysis mixture to reduce the breakdown of proteins into bitter peptides.

Selective Enzyme Use: Adding selected exogenous enzymes that do not result in bitter byproducts can help control the breakdown process more precisely, allowing for the selective degradation of non-bitter compounds.

4. Duration of Autolysis

Controlled Duration: Shortening the duration of the autolysis process can prevent excessive breakdown of proteins into bitter peptides. A shorter autolysis period should be balanced to ensure sufficient breakdown of yeast cells to extract useful components without generating excessive bitterness.

5. Substrate Preparation

Yeast Strain and Health: Starting with a yeast strain that is less prone to producing bitter compounds during breakdown can be beneficial. Additionally, the health and condition of yeast cells prior to autolysis (such as using freshly cultured yeast versus spent brewery yeast) can influence the flavor outcomes.

Pre-treatment: Pre-treating yeast cells with heat or chemicals to selectively inactivate certain enzymes before starting autolysis can help in reducing bitterness.

6. Post-Autolysis Treatment

Filtration and Purification: After autolysis, further refining the yeast extract through techniques like ultrafiltration can help remove smaller bitter peptides and other bitter compounds.

Adsorption Techniques: Using adsorbents such as activated charcoal during or after autolysis can help in binding and removing bitter compounds effectively.

7. Monitoring and Testing

Regular Sampling and Sensory Evaluation: Throughout the autolysis process, regularly sample the product and conduct sensory evaluations to monitor the development of bitterness. This will help in determining the optimal stopping point and adjusting conditions if necessary.

By carefully controlling these factors, the production of yeast extract with reduced bitterness is achievable, enhancing its palatability and widening its potential applications in food products.






Tuesday, January 9, 2024

Equipment and materials needed

 Equipment:

  1. Fermentors 500ml to 1L working volume, 10x--Our own 
  2. Fermentor 15L working volume--HKPolyU
  3. 磁力搅拌加热锅 5x big enough for 2L Duran bottle
  4. New centrifuge bottles--500ml 20x
  5. New 2L Duran bottles for fermentation GL80 2000ml 10x
  6. Stainless steel spargers 20x
  7. silicon tubings 
  8. air filters 100x
  9. Red caps 50x
  10. Air pumps
  11. Air distributors
  12. Microscope



Materials:
  1. Molasses
  2. Peptone?
  3. Antifoam A
  4. Papain
  5. Chemicals and reagents as listed in the tables below
Yeast culture medium:



Optimized Medium:

Mineral mixture:
Yeast extract autolysis:





Saturday, December 23, 2023

fingerprinting of yeast with interdelta primers

References:

Legras and Karst, Optimisation of interdelta analysis for Saccharomyces cerevisiae strain characterisation, FEMS Microbiology Letters, Volume 221, Issue 2, April 2003, Pages 249–255


Ness
 et al.,
1993. 
Identification of yeast strains using the polymerase chain reaction. 
J. Sci. Food Agric.
62,89-94.


Primer ordered:

delta2 5'-GTGGATTTTTATTCCAACA-3'

delta12 5′-TCAACAATGGAATCCCAAC-3′ 

delta21 5′-CATCTTAACACCGTATATGA-3′

Thursday, December 21, 2023

Fingerprints 20231221

 




Fingerprints 20231221



The results are quite good. However, we will need to improve the quality of the DNA extracted from the yeast extract for nanopore sequencing. What are the sizes of the markers?

We should try whole genome sequencing first and if not satisfactory, we may try AP-PCR-nanopore sequencing

Sunday, December 17, 2023

Workflows for 2023 HT Yeast Extract Project Phase 1

 Phase 1--December 2023 to May 2024

1A. December 2023 to 12 January 2024

  • Isolate and identify the yeast strain that is nearly identical to that of the Reference Yeast Extract
    • Streak from source for single colonies
      • YPD plates
      • Pick single colony
      • Observe under microscope
      • Grow test-tube cultures in YPD medium aerobically
      • Extract DNA from yeast cells
      • Extract DNA from Reference Yeast Extract
    • Interdelta Fingerprint comparison
      • Observe the patterns of lower bands
    • Nanopore sequencing for WGS
    • DNA sequence comparison-- target >90% similarity
1B. 15 January 2024 to 26 January 2024 
  • Lab-scale fermentor cultivation 
    • Medium follows the previous optimized recipe 
    • 4x500ml fermentors for as many times as needed for >20g of Yeast extract--Need about 10L of culture--5 times
    • Collect yeast cells by centrifugation
    • Pool enough yeast cells
    • Autolysis of yeast cells to make yeast extracts, following the previous optimized treatment conditions
    • Freeze-dry/oven-dry the yeast extract--check with Eliz

1C. 29  Janurary 2024 to 16 February 2024
  • Large lab-scale fermenter cultivation
    • HKPolyU fermenter familiarization
    • HKPolyU fermenter test-runs
    • >50g Yeast extracts production