ACS AMA: Hi Reddit! I’m Thomas Hofmann, full professor of food chemistry and molecular sensory science at the Technical University of Munich. Ask me anything about sensomics – research into how flavors make their way through natural and processed food to be smelled and tasted.

Abstract

ACS AMA

Hi Reddit! My name is Thomas Hofmann, I am currently Full Professor of Food Chemistry and Molecular Sensory Science at the Technical University of Munich (TUM), Germany. I also serve as Editor-in-Chief of the ACS's Journal of Agricultural and Food Chemistry. As Chairman and coordinator of an European consortium, I also successfully initiated the Knowledge and Innovation Community (KIC) ”EIT FOOD“ of the European Institute of Technology (EIT) in 2016.

Following my studies in food chemistry at the University of Erlangen-Nuremberg in 1989, I obtained my doctorate (1995) and completed my postdoctoral studies (1998) in the Chemistry Department of TUM. In 1998, I was appointed Acting Director of the German Food Chemistry Research Institute and elected a member of the Leibniz Society. In 2002, I was appointed as professor and Director of the Food Chemistry Institute at the University of Muenster. In 2007, I returned to TUM as full professor of the newly established Chair of Food Chemistry and Molecular Sensory Science. Since 2007, I have been a member of the ZIEL Institute for Food and Health, since 2009 Senior Vice President Research and Innovation, and since 2015 I have been Co-Director of the Bavarian Biomolecular Mass Spectrometry Center (BayBioMS).

My primary research interest is to decipher and re-engineer the combinatorial codes of odor/taste-active and taste modulating biomolecules creating the very authentic aroma and taste perception of foods and beverages, to utilize these codes as “molecular blueprints” to monitor process-induced changes in chemosensory profiles from the plant to the fork, and to control breeding and post-harvest processing parameters towards the development of preferred flavor signatures. To achieve this, my research approach coined “Sensomics” combines approaches from advanced natural product chemistry, food engineering, human psychophysics, chemosensory receptor assays, and bioinformatics. Please do not hesitate to ask me any question you may have on how our food’s odors and tastes are coded on a molecular level and look forward to a vivid conversation.

I will be back at 4:00pm CEST (10am EDT, 7am PDT, 2pm UTC) to answer your questions.

Hi Thomas,

Sounds like a very fun and interesting job! I have a few questions.

Do you ascribe to the idea of the five basic tastes sweetness, sourness, saltiness, bitterness, and umami-ness?

Do you think these five tastes are inherent limits to the molecular "code" / elementary make-up of food (so no other flavours can exist), or do you think they are just what humans have evolved to notice (like we can only see the visible light part of the EM spectrum) and there are more flavours out there, unknowable to us?

There is a strong negative association with artificial flavourings; do you think this is warranted, or are we missing out on some great flavour-food combinations because of the stigma?

Many thanks! Kal.

HerbziKal

Yes, there are five basic taste qualities identified today on the phenomological as well as genetic level. Next to the five basic tastes with one receptor for sweet, one for umami, one for sour, one for salty and 25 for bitter, we are equipped with about 400 olfactory receptors. Together, they open a huge horizont for combinatorial activation. Indeed, there is evidence that the receptors have been co-evolved with the chemical stimuli present in nature. For eample, the sweet receptor responds to sweet mono- and disaccharides and helps us detecting carbohydrate-(energy!) rich food sources, the umami receptor indicates the presence of essential amino acids in our diet, the salt receptor sodium ions helping us to keep sodium homeostatis, and the sour receptor resonds to acids present in unripe veggies/fruits as well as in spoiled food. The 25 bitter receptors primarily respond to pharmacologically active compounds and, therefore, aversive bitterness prevents us ingesting toxic components.


Interesting topic! I have always wondered what it is about garlic that smells and tastes so great going in, then stinks so badly for days after we've ingested it? I can't stand the smell of it on myself, or others, or in the house even, after a "garlic" meal. Also, why is it that garlic breath lingers so much longer than other offensive food smells, such as fish or cheese? Is there a workaround with garlic that mitigates the offensive aftermath, so to speak?

isthishowyadoit

After ingestion, some of the garlic odorants are metabolized to give allyl methyl sulfide (AMS). This AMS is the only odor-active metabolite formed, is circulated in the blood stream and then exhaled via the lungs, thus giving rise to the bad garlic breath.


I'm always amazed at how much we rely on a food's appearance to sort of "preload" our brains for what we anticipate we'll be tasting. How much of taste and flavor perceptions (ie what our brains tell us) are due to actual flavor reception (ie what our taste and smell neurons are transmitting) vs psychological factors of flavor anticipation.

In particular I'm thinking of that semi famous test (described here) done with white wine that was colored red. In that test, supposedly well trained wine tasters could not tell the difference.

RabidMortal

Indeed, our chemical senses can be fooled by other sensory inputs. In particular false colors induce another expectation in our brain that is then not met by the type of aroma or taste we perceive. These cases of "sensory incongruency" challenges our decision on what we really perceive.


Will there ever be a taste-o-vision? Much like a television but it will allow us to taste the meals in those food and cooking show.

Razasaza

This will be possible in the future. By means of flavor synthesizers, the odor codes of foods or any natural flavor may be re-engineered in real time to deliver authentic odor experiences. Examples are another dimension in cinema wher you can smell what the actors may smell. Another option may be odor messages send by your smart phone.


Is there any way to make a compound that causes "cool" feeling of menthol without the minty flavor? Perpetually cold drinks anyone?

Gonzo_Rick

Yes, menthol gives you a colling sensation by activating the TRPM8 cold receptor. The same receptor can be activated by a series of derivatives like menthol lactate or menthol succinate whicg show a drastically reduced odor activity due to the decrease in volatility.


Hi, thanks for doing this AMA!

My first question is about umami, that secretive sense... is there a scale that is accepted or even one that is arbitrary, like the scoville scale for heat? Are there umami sensors?

2) Why can cultures more prone to fermenting, deal with the smell of "rot" and is this quantifiable?

3) My mother has kidney damage, is there a spice or anything that tastes salty but isn't full of mineral salts or ions so she can enjoy saltiness again?

Bonus question: Why aren't IBU's (international bitter units) used more for grading flavors of things like bitter melon and spices like turmeric?

Thank you for your consideration, and I appreciate your AMA.

djabelek

To your first question: Yes, there is a heterodimeric T1R1/T1R3 receptor responding to the umami taste stimulus L-glutamate, and this response is enhanced by 5'-ribonucleotides, a hallmark of umami taste.

To your third question: such salt-enhancers are currently available, however, their activity is rather low and allows for a 20% NaCl reduction in foods only (one example are L-arginyl dipeptides). Currently, a series of programs are running globally to better understand our sense of salt and, on the basis of thiss, discover and/or design more efficient salt taste enhancers.


Would it be possible to greatly enhance flavors or the tasting experience by leading the brain through a specific sequence of flavors? For example, orange juice tastes horrible after brushing your teeth; or drinkable yogurt tastes great after eating something spicy. However, I am curious whether there is research into much more complex sequences to create a truly extraordinary taste experience.

EntreWisconsin

Indeed, the sequential combination of certain flavors are horrible, like tooth paste and orange juice. In this case an undesirable bitter taste is perceived that is mediated by bitter taste receptors which respond to the compounds in one food and are co-activated and/or allosterically modulated by compounds present in the other foods. However, most of the phenomena are not clarified on a molecular level and needs future investigations.


Hi!

In addition to the 5 receptors for salt, sweet, bitter, sour, and umami, I've seen some info about there being an additional taste sense for fat that only some people have. People think I'm crazy that I think good black olives have a creamy milky flavor to them in addition to their salty flavor, and I'm really picky about what milk I drink. Is the 6th taste receptor for fat a scientifically known thing that only some people have, or is it a myth?

AltForMyRealOpinion

No, there is quite solid science out there demonstrating that we are able to sensorially detect fat. Triglycerides could be shown to be hydrolyzed to generate free fatty acids by lipase released from the van Ebners salivary glands. Receptor proteins like GPR120 can then be activated by the free fatty acids. Interestingly, it could be shown that it is not the fatty acid receptor activation alone which gives us the fatty or creamy oral sensation. More precise, the fatty acid receptor activation needs to be accompanied by the trigeminal sensing of hydrocarbon moieties to induce an enhanced fat perception.


Thank you for doing this AMA!

As someone about to graduate with my PhD in chemistry and therefore in the process of exploring job opportunities in various fields, I would like to ask:

What analytical techniques do you use for projects such as this, and for what purpose?

chemgeek33

GC-MS/, LC-MS, 1D/2D-NMR, cell-based receptor assays, human psychophysical analysis, and bioinformatics


Hi Dr. Hofmann,

Two questions:

1) Would you please recommend a good taste/smell psychophysics textbook, or other resource for learning the basics.

2) How are tests done to best discriminate subtitle differences in foods; e.g., for testing different recipes?

Thank you!

SFepicure

A good book on psychophysics is: Sensory Evaluation of Food - Principles and Practices Authors: Lawless, Harry T., Heymann, Hildegarde

Another nice review on receptors and chemical stimuli is: Dunkel, A.; Steinhaus, M.; Kotthoff, M.; Nowak, B.; Krautwurst, D.; Schieberle, P.; Hofmann, T. (2014) Nature’s Chemical Signatures in Human Olfaction: A Foodborne Perspective for Future Biotechnology. Angew. Chem. Int. Ed. 53, 7124-7143.


I lost my sense of smell10 years ago and have been reading up on how the sense of smell works. Do you have any recommendations on papers relating to the mechanisms if how sense of smell works?

obiwan206

Schieberle, P.; Hofmann, T. (2014) Nature’s Chemical Signatures in Human Olfaction: A Foodborne Perspective for Future Biotechnology. Angew. Chem. Int. Ed. 53, 7124-7143.


Hi, Dr. Hoffman,

I've been interested in the science of food and taste for a long time. I debated going back to school for it, but I couldn't figure out what I would even do with such a degree short of working for a food conglomerate or academia.

So I have 3 questions:
1) Can you expand on the practical application of your work?
2) Besides McGee, are there books/authors I should be reading?
3) What are your thoughts on books like the Flavor Bible?

CompSci_Guy

  1. The Sensomics work can help to monitor quality changes on odor/taste on a molecular level in the food value chain from the farm to the plate, it can help to navifate plant breeding programs to identify premium tasting traits, it can be used to improve the taste of healthy foods with reduced fat, sugar and salt, it can...
  2. Schieberle, P.; Hofmann, T. (2014) Nature’s Chemical Signatures in Human Olfaction: A Foodborne Perspective for Future Biotechnology. Angew. Chem. Int. Ed. 53, 7124-7143.

How do you understand the difference between the 'flavour molecules' and the experience of tasting? I have worked in the wine industry and can provide objective analysis of a wine based on my subjective experience. Am I subconsciously noticing particular compounds or molecules during the tasting process do you think? Such as terpenes... What in your experience is the connection between taste and flavour?

DomesticApe23

Usually, about 3-50 odor molecules have been shown to create the aroma of each and every food. The experience of tasting now comes by integration of the sensory input in our brain and this is also affected by other sensory inputs besides taste and smell, like vision, texture perception etc.


Hi! I'm a recent BSc chemistry graduate and having read your papers on kokumi compounds, I'm inspired to take up a PhD in flavour chemistry or sensory science. What tips would you offer to someone of a non-food science background, who is looking to join the field?

bankaied

It is most importartant to have a chemistry background as Sensomics is in principle natural product chemistry on sensory active molecules. In addition, some training in sensory analysis and human psychophysics are helpful


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