Bulstrode,
Domestic or Intl flight? At that quantity it may have exceedded the 100ml container limit for intl.
If it was domestic. Nothing in the regulations prohibits the carrying of canned food on a flight. Can the screeners guarantee the integrity of every sealed food item that is loaded into an aircraft galley or is taken into the sterile area for retail?
It's a bit long winded but below is an extract of the Methods, Techniques & Equipment Version 4 which the screeners are bound to follow. I think in your case they may have overstepped their mark.
Call the aviation section of the office of transport security and get their take on it as well.
5.2 The methods and techniques to be used for the screening of goods entering a sterile area
(1) Screening officers performing the screening of goods going into a sterile area must carry out the methods and techniques to be used for X-ray observation of personal effects set out in clause 2.25 of this notice.
(2) Where possible, goods that are on pallets should be broken down to fit through the aperture of the X-ray observation equipment.
(3) Goods that cannot be cleared by X-ray observation equipment must be subjected to a physical search.
(4) The physical search of goods can only be carried out where the person has given his or her consent or the goods have been left unattended.
(5) When requesting permission to check the goods, the screening officer must not give control of the goods to the person.
(6) Screening officers carrying out the physical search of the goods must:
(a) if applicable, be aware of the reason for concern on the X-ray image, including the location of the uncertain item;
(b) inspect the goods, to an extent sufficient for the screening officer to be satisfied that the goods do not contain a prohibited item or weapon; and
(c) ensure that objects that prevent visual identification of suspicious or prohibited items or weapons are removed from the goods.
(7) If a suspect item has been located it must be removed and the goods subjected to re-screening using X-ray if possible. If necessary, the suspect item can be re-screened.
(8) If aerosols are detected at the screening point, they must be removed and physically examined. (The screening officer is not required to spray the item: a visual examination is sufficient.) If there is any doubt about the item after an external examination, screening officers will need to use their judgement to determine what further action might be necessary. This may include further examination of the item to establish its contents, prohibiting the item from entering the sterile area, or requesting the attendance of a law enforcement officer. The screening officer must refer serious or threatening situations to the supervisor or a law enforcement officer.
(9) Screening officers should also be mindful of:
(a) the weight of goods. Many items, such as pillows, stuffed toys, cigarette cartons, cosmetics and aerosol cans, are naturally lightweight. Any weapons hidden within such items would normally make the items unusually heavy; and
(b) any aspect of the goods that appears unprofessional or repaired, or shows signs of modification, tampering or external switches, batteries or wires.
(10) Where a physical search of goods is required as above, the goods being physically searched must also be subjected to screening by the use of ETD equipment. When screening goods using ETD equipment the goods must be broken down into the smallest reasonable units for the consignment
(11) If the items are fresh foodstuffs in trays and cannot be subjected to ETD for hygiene reasons then the goods must be visually inspected and subjected to screening using a hand held metal detector.
(12) When the items or goods are cleared, the cleared goods can enter the sterile area as long as those goods have not been mixed with uncleared goods, held in a secure location and there has been no unauthorised access to those goods.