Deleting inventory items will probably require you to remove many other tables of data as they are all linked.
You could start with the SQL query:
DELETE FROM SambaData2.dbo.PeriodicConsumptionItems;
DELETE FROM SambaData2.dbo.PeriodicConsumptions;
DELETE FROM SambaData2.dbo.TransactionItems;
DELETE FROM SambaData2.dbo.Transactions;
Which will remove the data that appears in the reports, it will not delete the actual recipes or inventory items but will clear the totals.