Is there any specific vedic/tantric science that deals with the preservation of food? i.e. methods use to preserve food that people used to implement in acient times?
As per Dharmashastras, oils (butter, oil, and fat), were a way to preserve food (as in keep something in its original state).
1.169. Food kept overnight, or kept for a long time, may be eaten if mixed with oils: as also preparations of wheat, barley and milk, even without, oils.
According to the Mitaksara, a commentary on Yajnavalkya Smriti:
"Food" eatables. Stale but if mixed with oily substances like ghee (clarified butter) &c., is fit for use though it might have been kept long. While transformations of wheat, barley and milk such as sweet-meat ball, (barley meal), cheese, inspisated milkJJ&c, though not oily and kept long, are fit for use. Provided they have not undergone any change (for the worse by being so kept).
In the Manu Smriti:
5.24. All lawful hard or soft food may be eaten, though stale, (after having been) mixed with fatty (substances), and so may the remains of sacrificial viands.
However, sometimes, food should not be preserved at all:
kṛta annaṃ paryuṣitam akhādya apeya anādyam || 17 ||
17. Prepared food which has stood for a night, must neither be eaten nor drunk,
śuktaṃ ca || 18 ||
18. Nor [should prepared food] that has turned sour [be used in any way].
Apastamba Sutra 1.5.17
4.211. [Let him never eat food given] by one accused of a mortal sin (Abhisasta), a hermaphrodite, an unchaste woman, or a hypocrite, nor (any sweet thing) that has turned sour, nor what has been kept a whole night, nor (the food) of a Sudra, nor the leavings (of another man),
5.9. (The milk) of all wild animals excepting buffalo-cows, that of women, and all (substances turned) sour must be avoided.
1.167. Food given without due respect, unlaw- ful meat, or which contains hair and insects ; or sour food or stale, or the leavings (of another man), or what has been touched by a dog, or on which a degraded person has cast his sight.
1.168. What has been touched by a menstruat- ing woman, or what has been publicly offered, food given by one who is not the owner, or what has been smelt by a cow, or the leavings of birds, or what has been wilfully touched with feet (these foods) let him avoid.
Therefore, fatty/oily substances may preserve food. However, food was sometimes not preserved at all when people followed these rules.