High-throughput screening for aroma production in food fermentations

A microtiter plate (MTP) method was developed to screen 1064 unique microorganisms-substrate fermentations for production of 68 target aroma compounds. Based on the number of hits identified by GC-MS, 50 fermentations were repeated at 50-mL scale in flasks. Comparison of GC-MS data showed that scaling up from MTP to flask did not generally result in large differences between the volatile profiles, even with a wide variety of substrates (juice, food slurry and food side-streams) and microorganisms (yeast, bacteria and fungi) used. From the screening results, Lactobacillus plantarum fermentation of chilli pepper was further studied as a high amount of phenols, especially guaiacol and 4-ethylphenol, was produced after fermentation. From HPLC-MS and sensory analysis, capsaicin was shown to be a probable precursor for these phenols and a potential mechanism was proposed. The protocol described herein to screen aroma compounds from fermentation of agri-food products and side streams can support development of clean label flavourful food ingredients.

Formalin attenuates the stress-induced increase in plasma epinephrine levels

Subcutaneous (s.c.) injection of formalin into rats is frequently used as a painful stressor that produces a three-phase nociceptive response. We have shown previously that s.c. administered formalin (0.2 ml of 4% solution per 100 g body weight) unexpectedly attenuated the increase of plasma epinephrine levels in rats exposed to exteroceptive stressors (handling, immobilisation). To clarify the mechanism(s) responsible for this phenomenon, the effect of formalin applications on epinephrine plasma levels was investigated in various experimental conditions. Subcutaneous application of formalin combined with exposures of animals to an interoceptive stressor, insulin-induced hypoglycaemia, significantly attenuated the stress-induced increase in plasma epinephrine levels, whereas plasma norepinephrine levels remained highly elevated. Moreover, administration of formalin to unstressed animals also manifested signs of an attenuated epinephrine secretion. Interestingly, intraperitoneal administration of formalin did not reduce the elevated levels of plasma epinephrine. We suggest that formalin attenuates epinephrine secretion from the adrenal medulla most probably via irritation of s.c. somatosensory receptors. We hypothesise that the irritation of the primary sensory afferents fibres might reduce the activity of the sympathetic preganglionic neurones innervating adrenal medullary chromaffin cells. Further investigations are required to establish whether the observed reduction of epinephrine secretion from the adrenal medulla is controlled by either spinal or supraspinal neuronal circuits.

Inhibitory Effect of Formalin Administration on Immobilization-Induced Epinephrine Release

Injection of formalin is used as a classical painful stressor that produces a biphasic nociceptive response consisting of a 1- to 10-min early phase and a later phase 30 to 240 min after injection. The period between these two phases, called "interphase," is characterized by attenuated nociception. We evaluated the response of catecholamine plasma levels to formalin-induced pain stress with special attention to these three time periods. Subcutaneous injection of 4% formalin (0.2 mL/100 g bw) into the hind limb produced a slight reduction of plasma epinephrine levels in the first 15 min, which was followed by a significant increase that remained high up to 120 min after injection. Norepinephrine levels increased immediately after injections and remained high from 30 until 120 min. To test the effect of formalin injection in a stressful condition, we exposed animals to 2 h immobilization stress. In the first experiment, formalin was injected before the start of immobilization. A significant decrease of plasma epinephrine levels was measured up to 25 min post-injection, whereas plasma norepinephrine levels remained high. A second formalin injection during immobilization was as effective as the first one: It depleted plasma epinephrine levels from 5 to 15 min post-injection without significant changes in norepinephrine levels. In the second experiment, formalin given after the beginning of immobilization produced a significant decrease of epinephrine levels 15 min after the injection and produced a significant increase 60 min after injection. The plasma norepinephrine levels were significantly increased by 40 min post-injection. The data show that the inhibitory process during the interphase of formalin test is able to significantly decrease epinephrine release not only during basal conditions but also during exposure to a severe stressor, such as immobilization without suppression of plasma norepinephrine levels.