Also, cleaning your sinuses with a Neti Pot and 1/4 tsp of sea salt and 1/2tsp of baking soda goes a long way to also killing smelly bacteria in the sinus mucous membrane.
I agree wholeheartedly about the bacteria in the back of the tongue producing bad breath along with a tonsil infection. Between the Neti Pot and the tongue scraper, you can reduce alot of breath odor. There's also an article in The Journal of Contemporary Dental Practice, that presents three studies carried out from 1992 through 1997 on the source of volatile sulphur compound (VSC) production and tongue coating. It highly supports the practice of tongue scraping for the longer lasting reductions in VSC levels. It identified several malodourous bacteria, such as Bacteroides, Fusobacteria spp., Peptococcus., and Peptostreptococcus, amongst the prominent cultivable microbiata.
Recent studies implicate the dorsum of the tongue as the primary source of VSC production both in periodontally healthy and diseased populations. These studies demonstrate (1) that removal of the tongue coating reduces VSC production and (2) when comparisons are performed in samples of mouth air following tongue scraping, tooth brushing, and rinsing with water in subjects with malodour, the longer lasting reductions in VSC levels are followed after tongue scraping.(1)
In the previous page, there is an article entitled, Fundamentals of Breath Malodour, The Role of Substrates, it explains the composition of saliva and the effects of an increased pH. TMA has an alkaline pH of 9.8, whereas the average pH range of both urine and saliva is approximately at 6.4.
Various authors have tried to reproduce the halitosis process in the laboratory by incubating saliva under different conditions. Saliva consists of a complex mixture of secretions from the salivary glands together with multiple species of bacteria, desquamated epithelial cells, leukocytes, and food remnants. Under healthy conditions, saliva does not have an odour. When its pH is increased, however, it turns into an increasingly putrefied odour.(2)
It would seem that since lemon juice has a pH range of 1.8 to 2.3, it would stand to reason that putting a few drops of sugar-free lemon juice various times a day on the dorsum of the tongue after tongue scraping in an effort to decrease the pH, thus creating an unfavorable environment for bacterial overgrowth. On the other hand, it's also imptorant to not let the lemon juice stay on your teeth for an extended period of time, as it may be harmful to the tooth enamel.