Uncovering Hidden, Unwanted Contents in Food-Species ID Testing as the Industry’s and Consumer’s Ultimate Solution

Thailand exports 4 to 5 metric tons of rice every year, more than half of which is jasmine rice, which could be twice as expensive as its counterparts. One would have concerns about the identity of the jasmine rice available on market – whether they contain pure jasmine rice, or are adulterated with other rice types that are much less expensive. Here we could easily understand how species ID could act as a reliable tool in determining the real identity of a rice sample. By the same reasoning, red wines from merlot grapes or cabernet sauvignon could be easily identified from each other.

The colorless, odorless and tasteless solid gelatin is prepared by prolonged boiling of animal skin, connective tissues or bones. Commonly used in the food industry as a stabilizer, thickener and texturizer, gelatin is added into foods such as jams, ice cream, yogurt and margarine. If not clearly labeled, consumers would be unable to tell if they are eating gelatin, which is derived from animal sources. To test for the presence of these contents, we would perform a type of species identification called “animal specific testing” (AS), which we could find widely applicable in the confirmation of animal species present in food to avoid fake products, confirmation of animal species absent in food, for example, to avoid animal diseases like BSE and AIV, to avoid food allergy, or due to religious concerns. It could of course be used also to confirm targeted animal species such as endangered species. Currently the most sensitive and specific testing available for performing AS are molecular methods such as DNA testing, or more specifically, PCR. To understand how powerful this molecular testing tool is, we would need to know what DNA is and the rationale behind DNA testing.

DNA and the Role of DNA Testing in Food

The words “DNA testing” might bring to mind Discovery Channel stories, but these molecular biology technologies are in fact routinely used in medical science and more recently by food inspection agencies. As a general background, DNA is the hereditary material found in all living things, including animals, plants and bacteria, and in some non-living things, such as viruses, and is different for every species of organism. For food testing, a DNA copying technique known as the “polymerase chain reaction” (PCR) is used. In this method, a stretch of DNA of known sequence for a particular species, e.g. sheep, is chosen. Very short stretches of DNA sequence, “primers,” which can match part of this sequence on the sheep DNA to be copied are made synthetically. These primers are only half a DNA ladder, as if the ladder has been cut longitudinally down the center of the rungs.

DNA is then extracted from the foodstuff and put into a reaction mix. This mix contains the sheep-specific primers and also molecules normally found inside a cell, capable of copying the DNA. Under highly specific reaction conditions, the DNA from the foodstuff also divides into two longitudinal halves and the primers can bind to the region they match.

Then the DNA is copied. This reaction is repeated many times until the stretch of chosen DNA is present in millions of copies. This DNA can then be detected visually after the addition of a dye. If the result of a PCR reaction turns out to be negative (but the DNA extraction reaction has worked as shown by the successful PCR of DNA known to be present), it usually means that the DNA of that organism is not present in the foodstuff. Using our example, if there is no sheep DNA present, but only that of the cow, then the sheep primers won’t match the cow DNA, therefore they can’t bind, and no copies will be made. Thus, the primers are the crucial element of this reaction, being designed according to the DNA sequence of the organism being tested for. They have to be extremely specific and highly sensitive.